I believe the closest PC GPUs, if anyone wants to do any comparisons online, are the ATI Radeon X1800 XL (for the 360), and the NVidia 7800 GTX (for the PS3). Not 100% sure how close those are to the "real thing" though. "Pretty darn close" is my impression.
I would like to point out that X360 games, since they always use the same GPU, can make much better use of the flexible pipelines of the GPU, than your typical PC game can with plain ole D3D 9/10. You'll probably notice that, in the vast majority of comparisons between these two cards online, the NVidia card is the clear winner, except in a few cases involving AA. Keep in mind the special mojo of having just that one architecture to work with, though. Its a bigger deal than you might think, and it plays well into the 360's hand, for many scenarios.
Sadly, with regards to the topic, most games fall into the general usage category, and not into the "we have the whole scene in memory, and there's not much going on, lets use some serious textures!" bucket that RB/GH fall into. The author of this blog post really needed to consider that the games he worked on were pretty special-case scenarios.
