I came across an interesting article in the Scientific American magazine (April 2007) which provides a Bayesian explanation to Gods existence/non-existence. I found another article with a better explanation, which I recommend you read.
Hundreds of years ago before the most basic physical laws were discovered, the ordered workings of the universe could be seen as implying an intelligent hand. A godless universe was necessarily disordered and p(U|notG,I) would be nearly zero for the observed universe. The existence of a god would then be the better choice. Morning glories needed a divine nudge to open after every sunrise. The planets needed to be pushed across the sky by angels. Eventually, science could explain these things without resorting to a god and the godless explanation becomes the better choice.