Like you say, they're rated somehwat differently because one's a console and the other's a portable.
But also they're rated on intrinsic value too not popularity. The Xbox is going to be most popular right now on it's release date. But I bet it will even out.
I was looking at cnet's ratings for the sony psp and the xbox 360, and noticed that the psp's rating was 0.3 points higher than that of the xbox! I know that they are scored differently, but still, it doesn't seem right. When I was in bestbuy the other day, the xbox 360 was relocated to the front of the gaming section and the psp was moved way to the back, and it wasn't even secured so that nobody could steal it! Write more later, Brian