We know how to do it. We know how to do it wrong, but we also know how to do it right. Normally we do a decent job of it.
Furthermore it isn't just one poll, every major poll that I've seen in the last few years which addresses any variant of this question has come up with the same basic answer. The more religious you are, the more likely it is that you support Bush. Unless all polling organizations have serious methodology problems (which I strongly doubt), the country is politically polarized along religious grounds.
:-(Incidentally that kind of polarization is a significant risk factor for totalitarianism.)-:
Cheers,
Ben