I think the main reason "Hardcore WOW players" (major contradiction of terms) have problems with other MMORPGs is that suddenly they are in a much more difficult environment.
WOW really isn't much of a challenge - just join the game, start your race to the top level, get there in around a month.
Be "the best" for a couple of months and then move on - 3 months of gameplay.
Hopefully the next generation of MMORPGs will bring back the challenge aspect where it will take time to get to the very top - nothing that is due out soon really looks like it will unfortunately.
If you call LOTRO much more difficult you have a serious problem.
