I don't have a link where they talk about it, it's just one of the philosophies that Arenanet has that I know about. They don't really want gear to be a major factor in your performance. You gear will still matter and play a factor, but less than it does in WoW, Rift, SWTOR.
There's even a plateau of power as you level, eventually a new level will no longer add as much to the power of the character.