Why do the politicians in US so much in support of religions (especially Christianity) ?

In communist country such as China, politicians do the opposite i.e discourage religions. I heard President Hu Jintao once said on TV: Stop believing in any superstition !!! Whereas in US elections campaign, both presidential candidates uses religion a lot. Has this to do with the fact that in a communist country with no general elections (non democratic country), religion is considered unnecessary to run a country since the death penalty is used to combat serious crimes.