I was wondering about this since I don't personally play LoL.
LoL was released almost at the same time as Heroes of Newerth. It came long after the original DotA still prevalent in Warcraft III and a limited number of other DotA games (can't remember the names but there were a few).
And yet, somehow LoL managed to stand above all other DotA games, despite starting on an equal footing.
I wonder why?