Fundamental Difference in Theistic depates

One thing I've noticed is that any time an atheist/secularist/scientist has a debate with a theist, the theist tends to look victorious. Why is that? Are we as observers willing to believe "god did it" as some kind of answer? Also the people on the science side of things tend to approach the issue from within their sphere of knowledge, things that they truly understand and feel comfortable backing up, (Dawkins within biology, Dennett from philosophy etc)whereas theists tend to say what ever they want to prove/disprove a point. It makes it hard for someone to defend their position if simultaneously defending biology, nuclear physics, cosmology, geology, and pseudo-science babble.