This is a big issue. I remember it took me a bit longer to get to 70 than most hardcore raiders, that seemed to all hit 70 on week one. By the time I was fully 310 geared and ready for "the next step" everyone was already demanding I knew every encounter if I wanted to join the raiding game. Learning groups were mostly composed of rejects without patience that would quit after a 2 failures.
In my case, I said to hell with it all, I just now logging in to get my weekly cap tomes, my detlascape normal rewards of the week, and then spend the rest of the week playing other games. It is not the game to blame, it's the community.