I haven't played RDR yet so I can't comment from experience, but it does sound like the PS3 got shafted a bit. Side by side there is a notable difference due to the lower res and type of anti aliasing used on teh PS3. But having said that, I don't think it looks like total crap, it could just be better. Well according to this video anyways...
YouTube - Red Dead Redemption: PS3 vs 360 Comparison