The wealth of knowledge about the nuts-and-bolts of theorycraft has never been more available. New players and old veterans alike have resources like WoW Insider, Wowhead, WoWwiki, or that juggernaut of theorycraft, Elitist Jerks. There are strategy videos, stategy manuals, and even a few strategy comics. The forums themselves have never been more informative, especially when you consider Ghostcrawler laying down wisdom all over the place. The information about how to play is out there for the taking.
And, c'mon. It's been about half a decade and near 12 million subscribers. Once you've done Nethekurse or Zereketh, you should know that you're not supposed to stand in pink, black, or red circles. Really, just don't stand in stuff. Is that really such a deep and meaningful skill that you have to relearn "Don't stand in stuff!" for Kel'Thuzad? So, if the Wrath raids aren't demanding a gear-based progression (meaning, it's all a gear check), then we should entertain the idea that we've gotten pretty good at not standing in stuff. That's certainly not the only raiding skill, but I'm using it as an indication that we're meeting the basic "skill" requirements.
Of course, even Ghostcrawler has acknowledged that Naxxramas is somewhat the new welfare epics. We know that Ulduar's going to be noticeably more "difficult." But until then, we could probably accept that the current accessibility of content owes some part to us getting better as players.