That's the problem.
Now we know not all consumers play games on their Macs, but its pretty impossible to get a game like Call of Duty running decently on a brand new $ 1799,- iMac, let alone future games. Hasn't got the CPU power NOR the GPU.
So for the same $ 1799 (middle iMac) there sould be at least a 1.8 GHz G5 in there with the Radeon 9800 Pro. Nothing special at all! All last year's technology.
Get the X800 (or 6800) in the upcoming PowerMacs and we should be on
par with the best PC's out there.
But we will have Mac OS X on them too!

(to compensate the extra cost

)