I've wondered the same thing. I thought perhaps blue has a slight advantage because the bottom lane on blue side can take golems before heading into lane at level one, yeilding a slight gold and exp lead, albeit a minor one.
Also, I think blue has a tad bit of an advangate when it comes to doing dragon. There jungle is attached to it, making it safer to jump out and steal dragon, or have a safe escape rout when killing it. Of course, the same applys for purple and baron, but baron comes later in the game, after two or three dragon kills. The early gold really makes a difference.
Those are just my thoughts.