Nope, sorry, they used mobile versions. http://guides.macrumors.com/Core_Image Now it doesn't specifically state the mobile nVidia cards. However, nVidia did have mobile versions of both of those cards.
ATI also has mobile versions of the current cards. So, again, they are most likely using the mobile version. Given the size of the iMac, the lack of airflow, and the relatively low power usage (200w, that display is easily about 120 itself), theres no way they could be using the desktop versions. Especially when you consider that most GPUs these days require a 300+ watt power supply and on top of that some require their own power connector.
My only complaint is that the video could be a little faster, or maybe it's a driver issue. I dunno, but I'd rather see a low end ATI/Nvidia integrated solution (if they must do integrated) than the Intel X3100.
The ATI X1250 and nVidia GeForce 7150m would both mop the floor with the X3100 while still being integrated and keeping Apple's profit margin high. Though I really don't see why we can't get even a 64MB GeForce 8400M GS (they do exist). If the last iBook had a Radeon 9550 why can't we have a GeForce 8400M GS?