"But W's personal religious faith is everybody's business."
If it (his faith) influences his political decisions, then yes, it most certainly is.
All human decisions of all kinds are the combined results of many, many different influences. So what? What influences your decisions? Something better than religious faith? What? I am getting really tired of this notion that it's somehow illicit for faith to influence decisions. Why shouldn't it? What would be a "better" influence, according to you?
I have two graduate degrees and have taught business on the university level for more than 20 years. I am also an Evangelical, and my decisions are profoundly based on my faith. If you think that makes them somehow inferior or less rational than they would otherwise be, then you are mistaken. In fact, my decisions are much better than they would be without my faith as an influence.