Check this out.

One man's struggle to get inside the many minds that make up Blizzard.

Clearly, the top dogs on the WoW design team have decided that the only viable mechanism for disseminating epic gear in a controlled fashion is raid content. Their logic is simple:

X = Time to beat raid boss (inc. garbage mobs on the way)
Y= number of players
Z = number of epic drops

Y/Z*X= approximate time investment for 1 epic drop.

Y=40 players
Z=3 epic drops
X=0.75 to beat boss

(40/3)*0.75 = 10 hours per epic from raiding.