The fact is Apple had a history of including lame to moderate gpus in the workstations. Let alone the iMac.
They can do better. I hope they do. *looks.
The ATI cards seem ok. Offering 'near' (re: outclassed) 8800GT performance for a cheaper price. I can't see how Apple could bung one of them in. I'd probably take it for now.
The next gen gpus are out around July by all accounts. And offering twice the current gpu SLI performance on one card. So. It is a waiting game.
In the meantime, I'm betting Apple shipping an iMac within the month. Gut instinct. And, if they offer something more than a 2600xt but less than a GT? I'm going to get it.
I don't like it either, but you're right - Apple always includes relatively outdated GPUs. ATI cards seem to have better Mac drivers, but they tend to run hotter than the Nvidia equivalents unfortunately. They, of course, can fit a better GPU in the iMac, and I imagine the next revision will have a better GPU in it. But it's always going to be a midrange and/or outdated card in the iMac as long as SJ is at the helm.
That said, I'm buying a 24" next revision if it has a 512MB of VRAM on the GPU. I'd even be fine with a 2600 as long as it had 512MB of VRAM - I've given up gaming on my Mac