Tank and healer needs SOME skills. Not much, but still. DPS doesn't need ANY skills. 5-mans from RFC to HC-HoR can be done even if 1-2 DPS are facerolling in ungemmed-unenchanted gear. And that's exactly what they do. If they would be tanks or healers, the group couldn't get past the first trashpack.
The game consist of
50% Utter crap who queue up as DPS.
~_o The goblin strikes!
Guild Wars 2, please don't break my heart. :(