If you have the money then buy a PC. If you can't stretch that far or don't want the complexity then buy a Sony PS. If you want most coverage then buy a PC and a Sony PS. I'm not sure whay people buy Xbox.
Another one is horsepower - it make sense to us because of our general understanding of what a car's mass is. 300HP car = powerful, 300HP dump truck = not powerful. Frustratingly, power to mass ratios don't seem to be very important to us.