The fact that the best ditch people not at their skill level also exlains why they call the game easy.
Johnny Awesome leaves behind everyone who doesn't measure up - and forgets about them completely. Johnny forgets that the people who stood in fire are still playing the game, and still standing in fire (and now don't have Johnny's help in beating the encounters because he's walked out and left them) all Johnny knows is that know he's found people who are as skilled as he is, the content just rolls over.
And if he did it, everyone must be able to, right?
You see it on the forums all the time. The solution to encounter difficulty is to kick your raid to the curb and find a better one. You even see it in the pvp players who KNOW that there can only be a set percentage of people at each rank. "Gladiator is ez, lol usuck" etc
What actually happens is that the top tier players get together and find the content easy, and everyone they left behind now finds it harder. When the disparity is too wide, blizzard have to step in and adjust the game so that the discarded can still play (they need the sub money) and then the very good players are up in arms at the changes because after all the game is far too easy.
The other major error I see is that people completely and utterly forget that wow is a game, not an objective test. The purpose of wow is to entertain it's audience. The actual audience of real people who "aren't very good" at playing the game, not some theoretical audience of perfect players who can play 24/7 to progress.
Based on the current numbers of clears and the availability of pugs and so on, wow is already far too hard for the people who actually play it. Content tuned for it's real audience is the right way to go. Ignore the extremes (the very good and the very bad.)