Dude, this is not the is God real topic...
All religions are man made... they must be.. that is their nature. The point is when you see an aspect of faith that is common to many religions around the globe that had no way to communicate a thousand years ago... that aspect must be more credible. The differences are what man added in an attept to wield the power of the church for their own reasons.
wait, why are religions man made? are you saying that people interpret gods and make a religion based around what they perceive and feel about the gods? because all religions that I know of are based on gods, so they aren't originated by humans...
anywho, I've heard about the three religions one god things before and I, as a Christian, pretty much see how it works. Although because they are different only one of them can be real...