~40% according to WarcraftRealms. Of course Level 80 characters are likely to be over-represented as they'd average more time logged in and thus be more likely to catch Census sweeps.
So those numbers actually sounded perfectly reasonable to you? Nothing went off in your head such as the fact that WoWJutsu only tracks guilds whose members are toting raid gear? It hardly comes as a surprise to learn that raiders raid.
Of course, such folk make up most of the playerbase.
My point isn't that everyone raids, my point is that those who want to see WOTLK content have ample opportunity to do so. It doesn't take long these days to level a character to 80, even if you're extremely casual, and Naxx pugs these days are not very discriminating. Quite frankly, if you're a guild (as opposed to a random lost soul with no guild who does nothing but pug on a small server) "struggling with Naxx", I'm not sure why that would be.
The comment about Blizzard wanting the make the game more "casual friendly" is true, before WOTLK only a small percentage of people cleared BT and even fewer had been to Sunwell. More people have done it post 80 than pre. Heck, many BC raiders didnt even get to see beyond Gruuls/Mags/ZA. But I think the hard modes of Ulduar really are challenging. CC is back into play again, there is less aoe trash. They really tried to do a few things differently, I can appreciate that. There are a few people on my server who have downed heroic EZ Yogg and are like "that's it?", neglecting the hard modes and end boss. It's a whole different level of skill, I'd be surprised if more than a couple of guilds per server are clearing him before Icecrown or whatever the big patch is that will likely come out later this year.
The only thing I wish they'd done better in Wrath is world PvP. I enjoy Wintergrasp, don't get me wrong, but a Halaa-like town or Plagueland/Terrokar-style towers would be nice. Ones with real incentive beyond XP bonuses that would inspire 80s to play. The new BG sounds neat though.