The reason that you solo Top is because it gives you more dragon control.
The reason that you solo Mid is because mid is farther away from dragon than bottom is.
The reason that you duo bottom lane is because roaming was proven to be ineffective.
The reason that you jungle is to give top lane an experience advantage.
The reason that you use 0-CS supports is to give your bottom lane a farm advantage.
A 1-1-2 lane setup is the only thing that fits the current meta, and the only thing that really makes much sense.
The only thing i see wrong with the 1-1-2 setup is that the Blue team has a marked advantage in their jungle setup.
Basically, if your top lane heavily assists the jungler with wolves/blue buff (basically 2 man jungle, steals xp and all, gives jungler the kills) and your bottom lane kills golems (Support Leashes, and then heals the AD carry up to full before they get to lane.) then the jungler's Golems will be respawned by the time he gets there, and both bottom and top lane will be halfway to level 2 before minions get to lane.
It's something that sometimes happens in europe, and some people steal small golems in US.
The reason that you solo Mid is because mid is farther away from dragon than bottom is.
The reason that you duo bottom lane is because roaming was proven to be ineffective.
The reason that you jungle is to give top lane an experience advantage.
The reason that you use 0-CS supports is to give your bottom lane a farm advantage.
A 1-1-2 lane setup is the only thing that fits the current meta, and the only thing that really makes much sense.
The only thing i see wrong with the 1-1-2 setup is that the Blue team has a marked advantage in their jungle setup.
Basically, if your top lane heavily assists the jungler with wolves/blue buff (basically 2 man jungle, steals xp and all, gives jungler the kills) and your bottom lane kills golems (Support Leashes, and then heals the AD carry up to full before they get to lane.) then the jungler's Golems will be respawned by the time he gets there, and both bottom and top lane will be halfway to level 2 before minions get to lane.
It's something that sometimes happens in europe, and some people steal small golems in US.
Tri lane for life.
^ This is only true because it hasn't been countered yet, but that's the current way of things.
Jungling also is not done simply to give top lane and experience advantage.
It also puts more gold in your teams pockets (Provided your top lane farms well, this is why you want your solo top lane to be one of your best players) by adding jungle creeps to the gold count.
And also, very importantly, it provides map control, and further strengthens control of dragon. If one team has a jungle and the other doesn't, you forfeit dragon control.
If your team has the stronger jungler, and you're not worried about Dragon, you can send your 2 champs top and solo bot, and deny their solo lane farm if they don't switch lanes.
If they -do- switch lanes, you immediately control dragon because you know your jungler will beat theres in regards to getting the dragon.
It's not a set in stone format that has been proven best.
Much like the rest of the meta game, there are counters, but whether or not they have been discovered is a different issue.
Jungling also is not done simply to give top lane and experience advantage.
It also puts more gold in your teams pockets (Provided your top lane farms well, this is why you want your solo top lane to be one of your best players) by adding jungle creeps to the gold count.
And also, very importantly, it provides map control, and further strengthens control of dragon. If one team has a jungle and the other doesn't, you forfeit dragon control.
If your team has the stronger jungler, and you're not worried about Dragon, you can send your 2 champs top and solo bot, and deny their solo lane farm if they don't switch lanes.
If they -do- switch lanes, you immediately control dragon because you know your jungler will beat theres in regards to getting the dragon.
It's not a set in stone format that has been proven best.
Much like the rest of the meta game, there are counters, but whether or not they have been discovered is a different issue.

http://www.mobafire.com/league-of-legends/build/duffs-336706
Come hang out when I'm streaming! http://www.twitch.tv/dufftime
Also I forgot to mention, mid lane has the shortest distance between it and the tower, so you can stick a squishy in it, without the need to support it quite as much due to the safety of the tower.
That's another reason mid lane is not usually a duo lane.
That's another reason mid lane is not usually a duo lane.

http://www.mobafire.com/league-of-legends/build/duffs-336706
Come hang out when I'm streaming! http://www.twitch.tv/dufftime
You need to log in before commenting.
the duo is on botlane because ganks are less effective on a duolane
lets say u run your ap bot and your adsupport mid. Your ap will lose immense amounts of farm because hes to vulnerable so far away from the tower. thats why the sidelanes are always duolanes! you are less exposed to ganks with a partner/babysitter
greez sam
But with the 1-2-1 and a jungler setup mid won't be able to leave for ganks, and if some one from top or bottom leaves then the have a 1v1 with the enemy laner underleveled, also with a lot farther to travel for gank, giving MIAs more time to be called and notice to be taken. The only problem with that is if they have a jungler as well.
But what you says is true, its a lot farther to extend out in top and bottom, more bushes which are closer to hide in for gankers, and if they do push to turret which they probably will then it's harder for you to last hit and get your CS up. That can make a large difference.