It depends on the dsp mode you are using, and what you are listening to.
For music and 5.1 channel stereo, the center channel gets a mix of the left and right, and will need to handle the same peaks, so it needs the same power.
For 2.1 tv running in dpliix, I'd say your left and right would probably need more power, as the fronts would handle the peaks and the center, the mid range.
For DD;DTS 5.1 and higher dvd/HD, I'd want equal power to all speakers, even though the front two will use the most power. The center will take most of the dialogue, but midrange doesn't need that much power. There's not too many peaks in dialogue.