solo mid = more xp and gold = more powerful carry = win

2 person mid is still better than solo mid, because it's easier to gank/assist outer lanes that way.

But LoL players seem stuck in their ways (Even if they're less effective) so whatever

Generally speaking, whoever goes mid (at least with the old xp system) is going to be several levels above the other team with substantially more money. In LoL, a single buff carry can completely dominate a team fight, especially if they have the level and gear advantage.

It's important to have your solo in mid because solo is solo for farming reasons and farming reasons alone. Now that you have your farming carry in mid solo, he can easily move to bottom or top lanes and assist in a gank or easily have top or bottom lanes come to mid to assist in a gank at mid if the solo is struggling. It's solo mid because the map is bigger than dota and having teammates quickly moving from or to the mid lane is important.

1) The carry benefits from increased exp gain (not having to share it) and from higher potential gold farming (not having to share last-hits)
2) The middle lane is safer, and is thus more suitable for late-game powerhouses that are not as strong early game.
2a) The bushes to sneak attack from are farther from the creep battle.
2b) The towers are closer together, you have less distance to run.
3) As the game progresses, the carry is going to want to gank for kills. Being in the middle lane gives him 4 possible targets with a minimal walking distance instead of 1. (Assuming the people IN your lane are smart enough to avoid being ganked by you.)

Um. Solo mid was the norm in DotA, too.

Because in the middle lane assuming you don't over-push it you are never outside of flash distance from your tower, where the top and bottom lanes you are and therefore are more easily ganked. On top of that with how small the map really is, you can go top to bottom or bottom to top in under a minute while staying out of sight and with the new xp changes wont get hurt as much in gaining xp by missing out on some creep xp to help gank someone 2 or 3 levels higher then you in the end. In the new meta game it is more rewarding to gank the higher level player then pick on the feeder.