The PS3 really IS better than the xbox, but it also costs like $700 or so to manufacture. It only costs $300 ish (i forget) because they expect you to buy at least $400 worth of games.
Xbox is a similar deal, where it costs them a little more to build it than they sell it for, but it really isn't designed to be as powerful. It really isn't all that important to have the more powerful and expensive thing. I personally have an xbox and I am happy with it, expect for the fact the network isn't free.