I just got out of a game with a jungle Heimerdinger, Top Irelia, Bot Nunu+Kogmaw, and myself Mid as Veigar. It was a loss, but I believe it was only so because Nunu and Kogmaw were pushing bot when the entire enemy team zerged through mid inner tower, inhib tower, inhib, and nexus towers.

Anyway, Kog and Nunu blame me for not ganking bot (Kog ended with 7 deaths). They say "The enemy team had jungle and mid presence in bot lane and we didn't", even though the enemy mid (Vladimir) never ganked bot either and the enemy jungle (WW) only ganked once. They say that they would have won their lane if I ganked.

However, I know Veigar is like Nasus in that he needs to farm his Q as much as possible in lane. Even without that, Vladimir was pushing mid like a madman and would certainly have gotten the tower down if I left to gank bot. Even without THAT, I was told by the enemy bot lane (Ashe+Galio) that they had constant wards up.

I ended up getting 100 on my Q by 25 minutes, and having 2 doran rings, sorc boots, Deathcap, Deathfire grasp, and Fiendish Codex. My scores were 4/3/2.

So, tell me: Is it a given duty of mid lane to gank the other lanes, even if you are a farming mid like Veigar?

EDIT:
Enemy team was: Top Udyr, Mid Vladimir, Jungle Warwick, Bot Ashe and Galio

If you can both push mid lane AND have good mobility (fast speed/tele/ghost) you can gank top/bot lane if the enemy has pushed.
Otherwise just farm.
Basically gank if you can do so and still be back in your lane before enemy pushes/farms too hard

Depends on who you are playing. Good champions that can shove a lane out and gank are Kassadin and Ahri. Another champion that cant really shove a lane but can gank really well is fiddlesticks. But overall, no mid should never HAVE to gank bot.

well i rarely mid but sometimes when i use veigar/tristana/fiddle so.. this is my opinion.. first thing of course we must see the situation first.. if there is 2 champ in mid who will ever gank any other lane.. so maybe if your lane is safe or you've destroyed the outer turret you can gank anywhere.. second thing.. if your team in bad condition and your lane is in good condition and maybe your foes is in bad shape too.. why no? just try for fiddle he can use his terrify or his ult and tristana rocket jump and ult and veigar use his stun.. well its up to you.. you can just gank or stay in your lane and farm.. nothing is a must here.. basically.. i think.. if there is foe in mid.. you should never leave that lane.. or it will be doom if you dont have good jungler..

IMO, if your laning opponent does have bot presence, you should be trying to gank bot. If they're bot, they won't be able to push your tower, and you can try and countergank. Otherwise? No, you don't have to, nor are you supposed to. If you see a good opportunity, great! If not, that's fine too.

The number 1 reason to having solo lane is the level advantage. So if you are constantly leaving mid to gank you will get under leveled and the other mid if they are good will capitalize on this and push you even deeper into the hole of being under lvld or even worse kill you.

The only time I leave mid is if they leave or if I kill them. Otherwise I tend not to stray from mid unless there is a random fight going on in the jungle/river.

lol

Very true; I played against a Veigar mid a couple games ago while I played Katarina. He left his lane so many times to gank and I ended up getting 3 levels ahead of him and killed him each time he came back to lane. I also ended up going 23/0/9 because of this mistake that the opponent had made. DO NOT GANK IF YOUR LANE IS PUSHED BY THE ENEMY CHAMPION; if you are planning on ganking then push your lane and then leave if you have a champion with some form of mobiltiy; otherwise just keep your lane stable and farm.

It really depends on my chance of success and how my mid is doing. Generally, when I play Swain I'll gank bot because it's easy to push back and I have CC to assist with the gank. If bot is pushing, I won't turret dive or say anything. I figure if they are pushing, they must have the lane in control.

Although, when I play karthus I tend not to leave lane except farm jungle when I've pushed mid too far. I'll use R to assist with ganks and take the assist if I know it's likely I won't use it for a little while.

Really, if you can do so then do it. If you can't, than don't. Remember, if you help bottom too much your lane may fall or you'll fall behind mid-late game. You'll get yelled at for losing your lane and being "useless" because bottom didn't need your help anyway.