Magic Magnum said
What in the world is the point of laning? Why does which line I run in matter depending on my build? They all seem the exact same.
I guess it just has to do with the way the map is set up. Technically, you could try to bum rush mid as five - it might work against a less coordinated team. But towers in League are strong, so a few people could defend against your siege while your outer towers are left undefended, and that means inhibitors are in danger.
There isn't any clear reason for the current lane meta, but there are a couple justifications for the way it is now:
Putting your marksman/support bot instead of top allows you to contest dragon more easily, which is important early game when trying to snowball a lead. Mages scale better with levels, while marksmen scale better with gold (damage coming from auto attacks). The support leeches EXP from lane due to minions dying near them, so it's more ideal to put the mage in a solo lane. They can level faster and then roam top or bot for ganks, which is especially good if your mid is an assassin. @Rare: League is much more fun with friends! There are a lot of details to playing that aren't intuitive, especially if you've never played a MOBA before. It's a way better experience to have others show you the ropes while you play.