Lets try this again:

1) Why is there an AP Carry mid?
AP Carries tend to farm with their abilities once the mid game is reached. This, plus a feed on blue buff, allows them to push waves and roam with the jungler. They can clear farm quickly, and therefore lend to map presence. The reason there is an AP carry at all makes it more difficult for players to simply "Build armor and win." Their combination of utility and damage output forces players to make decisions on itemization beyond "everyone buy a thornmail and win the late game". Furthermore, AP Carries tend to have some form of mobility/cc built in (with certain exceptions of course) thereby, despite their squishyness, allowing them to sit in mid by themselves because it is the shortest lane from outer turret to outer turret. When I jungle I frequently call upon the mid player to help me counter-jungle buffs.

2) Why is there a support+adc combination bot.

The ADC is less flexible and cannot farm with abilities such as the AP Mid, therefore it is somewhat impractical to run them in the middle position because they would not be able to take advantage of the central position to increase their map presence. Therefore, they are in an extended lane. Furthermore, most ADC have less utility/cc/escapes built in than AP Carries, so putting a support in a lane with them gives them that utility/cc/escape that covers them from ganks and allows them to disengage from a bad fight. Finally, as to top versus bot, while the recent finals have shown a fair bit of top play from the adc/support, the primarily reason I believe is simply Dragon control.

3) Why Bruiser/Tank top?

The Bruiser is effectively a mid-game position. This champion is there to ensure the team has a little bit of everything needed to win midgame fights before the ADC/APC damage is dominant. You find that bruisers typically underperform in the late game unless they have some form of strong initiate and built more towards tankiness or a strong gapclose and stickiness to kill carries coupled with more damage. The reason you play a Bruiser or Tank top is that they will have a bit of utility, and enough hp and armor to make them survivable on their own in a longer lane.

4) Why have a jungle?

There's a few reasons for this. If you ran a double top you'd be crippling yourself because your top would receive less experience and if both are farming, gold, than if you had a solotop. Furthermore, running a tank/supp top means there is no one to control map objectives and feed buffs to the lanes. There is also the fact that you would effectively be not taking advantage of a great deal of money/experience that is sitting on the map unfarmed by your team. Finally, the biggest reason is map control. A good jungler will be carrying oracles and be warding, thereby denying the security that wards provide to lanes, and helping snowball the carries early with protective counter-ganks and ganks on lanes that are easier to kill/drive out of lane. The jungle is the primary source of map presence in the laning phase. It is also probably the most misunderstood and poorly executed role in low-elo gaming.

5) Why are there no other viable meta games being played?

It's hard to see a meta that would be more successful than the current one for the reasons I just listed. I understand running adc/support top if your nexus is on the upper right side as that lends proximity to red buff, but beyond that there are few advantages towards shifting this meta from my vantage point.

tl;dr Well ****ing read it because its too much to summarize.

a lot of other people have said the reasons for lanes being as they are, id just like to differentiate from dota a bit,

First, AP, AD, and lol's other stats are about as different from STR, AGI, and INT as they can get, i have played dota for a whyle, and i still have no idea how it works, but i will say that stats, the gold to item ratio, and the way you lane are all very different.

Second, gold. denying creeps does not exist in LoL, neither does loss of gold on death, this means that champions can go and raise gold on very different levels, farming is effective even if you die, etc, this changes the meta also.

Third, EXP sharing. EXP in lol is devided between all players within the EXP range, whereas in DOTA all players in range are given the same amount regardles, this means that each player in a duo lane gets 1/2 the exp of players in a solo lane, and trilane gets 1/3 of solo lane EXP, making it so that tri lane players will always be underfed, and duo lane players will always be behind solo lane players by level, and costing your team valuble EXP from an extra lane if you do not have a jungle.

These are just a few things about LoL that differ from dota and help to explain the meta a little bit, hope i helped.

As confusing and stupid as one might find the set up of the LoL "metagame." It is quite simple. There is only 1 LoL metagame and there will only be 1 LoL metagame. You can think of your own strategies and tactics, but in the end, the game setup, map, lack of diversity between all heroes, oh sorry "champions," will keep the "metagame" the same forever. Everyone is too noob, or the rewards of doing something else are too small to be worth doing something different. this is league of legends: A game where everyone plays the same champion, chooses ignite and flash, goes to the designated lane for their role, and dicks around. No trilanes, no different champions, no different tactics. If you want these things, come play Dota 2.

1- Who is supposed to ward? (In DoTA it was a support only job, but in League i see both bruiser and AP dmg dealer buying wards every now and then).

MOSTLY the support but everyone(save the ADC, and then even than..) should grab a ward or two. In S3, they upped the gold per second across the board so supports NEED to be getting items now. They just have to much gold not to. So, other roles help them out. Especially early on.

2- Is there a guide for right ward placement? Or i should just thrust my instincts?

Yep. Lol Pro has a great one. BUT it sounds like you have extensive experience warding in DOTA, so your instincts are probably good. (Keep in mind you CAN ward inside Baron, unlike Rosh)

3- As a bruiser (thank GOD you don't use the "tank" term either, i hate it so bad...), I should start the fight? And inmediatly after it, focus on the enemy AD carry? I guess this actually depends on the type of champion and general lineup, so feel free to avoid this question!

Yah, dodging this one :P Generally, yes but...jesus so many team comps and such. Deoends on your team. Also, tanks are for MMOs. Silly term.

4- How about runes? When should i start filling some pages? I have about 4-5 tier 3 marks built for a Nocturne AD build right now. I am summoner level 21 or so.

ONLY BUY TIER 3 RUINS. And personally I picked 2-3 champs and got runes for them first. The other (good) option is too have a generic page for each role.

5- When does Dragon spawn? And how much minutes do i have to wait to kill him once again? 190 gold for the entire team seems pretty good if a team manages to get him every time he spawns.

^ This right here. Good extincts. Smart player. It spawns at 3 mins, 2:30 I think and respawns every 6 mins.

Uhmm i think this is quite all for now. Thanks again for your consideration!

This statement is false. The meta has ACTUALLY been flcutuating since the game's been out. It's stagnated recently but it changed for years.

AD Carry mid? Bruiser with support? People still do that, right? The European players didn't come out of left field with ADC/Support bot, stomp people and than the meta changed. Right. It's AlWAYS been that way.

Everyone picks the same champs in the same spots? Man, people were just playing KZ Mid ALL the time. Everyone did it. EVERYONE. Oh wait, no they didn't. Until pros started doing it and ROFL PWNING with it.

Jayce man, EVERYONE played that guy before World Cup. EVERY GAME HAD A JAYCE. Wait...not it didn't. Other than release he was "UP" and abandoned in favor of the flavour of the month.

It's not the game, it's the players. DOTA(carried over into DOTA2) has been around a helluva lot longer than LoL and is, honestly, a totally different game. It's a waste to try and compare the two. Both are awesome and different in there own way.

Also- Meta changes don't come from the bottom, they come from the top.

(No excuse me well I got clear the sarcasm out of my throat before I choke on it)