The PS2 version was heavily reworked and still had several, very large and noticeable, downgrades ... and the PC version required a high end Geforce FX (Geforce 5) to play the game at a similar quality level to the Gamecube, while the XBox 360 only had a modified Geforce 3 GPU.

It was an old IGN Xbox article. I'll have to find it. I didn't realized they've removed the X-box channel completely. When I find it, I'll post it. As for PS2 RE4 comparision, you do realize that the GC version of the game had double the polygon count right? Leon's model was 10,000 polygons on Gamecube and 5,000 on PS2. In additon the PS2 version has lower resolution textures and nearly all of the real time lighting effect removed. Some of the real time cinematics of the GC version were the full motion video cinematics for the PS2 game.

The Xbox was undoubtedly the strongest system (from a technical standpoint) of the last generation, but I agree that some games that were tailored to certain platforms had to be reworked significantly to be 'ported' to other systems. Last generation, the advantage that the most powerful console (XBox) had over the least powerful (PS2) was minimal compared to previous generations, such as the Atari2600 generation (where the intellivision and collectovision were both superior, albeit newer). That said, I can believe that a ported GC game would run choppy on an Xbox if it wasn't reworked to fit the hardware, simply because there wasn't really an enormous amount of horsepower difference between systems last generation.