The center could have been used more and then people could choose whether to emiminate the center and send that signal to their fronts if they wished.. but the way they've done it is stupid for many reasons, namely, the whole idea of 5.1 is to use all channels. Saying it sounds better without center is a cop-out. And it removes the listener's choice of customizing if they were to feel it sounded better divided among the fronts.
Right, let's put this customizing thing to bed, shall we? First of all, when they mix a vocal into the center channel or mix the vocal into the front stereo channels - these require two sets of different mixing techniques.
So, in other words, if you have a vocal in the center and then downmix that center channel into the front stereo, it won't sound as good as a properly mixed vocal in the stereo front. And in a lot of cases can cause problems with the clarity of the vocal not cutting through anymore. Whereas the front stereo mixed vocal will be fine for all 4.1/5.1 users.
So, there is no choice either way. Only a compromise in both mixing situations. They chose one particular path. But if you listen to The Game DVD-A, you'll notice that the center is used in some songs. Most notibly the opening track.
Also, just because you mix in 5.1 doesn't mean you have to use ALL the channels. Sub and center are optional for some. It's all about how they wish to represent the material best.