One thing to know about PC gaming, most games are being ported to or from consoles (mainly the xbox360). I can't image those systems aren't nearly that much more powerful then those cards.
Well, the thing about games that are on both the Xbox360 and PC is that they both use the same tools, such as DirectX. Despite the different architecture of the CPU (PPC in the Xbox360, x86 on the PC), the use of the same tools essentially makes any "port" native development on the PC. For instance, GTA4 is incorrectly called a "port" on the PC, even though the Rage engine was natively developed for the PC alongside the console versions. Nearly all games that come out on PCs that are also on consoles are made by companies using multi-platform engines and tools, so calling them a port is not exactly accurate in the traditional sense of the word.
On to GPUs. The 9600M is basically a slightly faster version of the 8600M in a newer non-defective package. The 8600M was a DirectX 10 and slightly faster version of the 7600 "Go". If you compare benchmarks, they're largely the same. The 8600M GT outscores the 7600 Go GT in some benchmarks, while the 7600 outscores the 8600 in some.
The GPU in the Xbox360 is basically the equivalent of the Radeon X1950 (desktop version), while the PS3's GPU is between the 7600GT and 7800GT (has features from both, same generation as the Radeon X1950, nvidia's equivalent GPU to the X1950 for that generation was the 7950 GTX).
When you consider just how much faster desktop GPUs are compared to the mobile versions of the same name, it doesn't take much to realize that the Xbox360's GPU is several times faster than the current GPUs offered by Apple, and even the PS3 has some speed on Apple's systems.
Xbox360 games, except for a small few, generally run at 720p native with 4x FSAA. Halo 3 is rendered at 640p because of "lighting effects" and Modern Warfare 2 (both console versions) is rendered at 600p, but the Xbox360 version has 4x FSAA. For the most part, Xbox360 games that are also on the PC run at the same "high" settings the PC version does. Theres no way you're going to get a 9600M GT running Modern Warfare 2 at 600p with 4x FSAA, everything set to highest, and still maintain the same 53fps average the Xbox360 version runs at. Theres also no way that 9600M GT will run GTA4 at 720p (Xbox360 version runs at 720p with 4x FSAA, PS3 version is 640p, no FSAA, but has a full screen blur filter), 4x FSAA, and the same detail settings while being able to maintain the same 30fps the Xbox360 does. Theres definitely no way the 9600M GT would be able to push Forza 3 (if it was on the PC) at 60fps, 720p native, 4X FSAA.
Yeah, it could run better. Even things like GTA4 run fine on the MBP. Yes, they could run better, but there seems to be this massive leap between "normal" games and.. Well, Crysis? Running games at ~720p helps, and looks nice with 4xAA etc.
Yeah, but theres no way that 9600M GT will be able to maintain 720p, 4x FSAA, and the same high texture detail settings, as well as full reflection, water reflection, and other lighting details. The 9600M GT simple doesn't have the memory bandwidth or horsepower. And like I said, its certainly not going to run Modern Warfare 2 at the same 53fps average, 60fps peaks the Xbox360 does at the same "highest" settings with 4x FSAA.