If you can't play WoW with all settings turned up on modern Mac hardware, then there is something wrong. The game is nowhere near as graphically demanding as say EQ2.
Yeah, but as has already been pointed out, the 24" iMac's native resolution puts quite a strain on the system's resources.
The HD2600 is a mid-range graphics adapter, and it's not powerful enough to decently run recent games at 1920x1200. People running WoW on 20" iMacs apparently don't have that kind of trouble.
On the other hand, I've seen Oblivion and The Witcher on a 24" iMac, and both were running quite well, so YMMV.
I want to get a notebook pretty quick here but with all these reports of 3 year old games running like crap on modern hardware, I can't help but look at other companies (but what though? HP? Never a Dell. Sony maybe?).
I sure hope the ability to run games stops sucking in OS X.
I got a 15" MBP back in June (2.4 GHz, 2 gigs RAM, 8600 GTM w/ 256 megs), and it's a decent gaming rig. I've been playing Overlord, Neverwinter Nights 2, Titan Quest and The Witcher, all running at 1440x900 (native resolution) with most or all options on.
I haven't really gamed on OS X, though, and since I quit WoW quite some time ago, I can't say how well it runs on a MBP, though there are plenty of other threads on that specific subject.
Most people go with iMacs because they're essentially the most powerful all-in-one system, they come with OSX, and they're much more reliable than anything else out there.
OS X is certainly one of the main reasons, along with the fact that the iMac is damn sleek.
Reliability, though, both hardware and software, seems to have fallen much lower on the list of Apple priorities in recent times ...