Well, Islam does recognize the other prophets and their religions (so that includes Judaism and Christianity). And I don't agree with the fact that "it was around even before that", as people didn't fast regularly and in the same fashion as jews/christians/muslims do.

And IMHO, belief doesn't have to be totally separate from reasoning. We're human beings, our beliefs are definitely influenced by what our reason (among other stimuli) dictates us.

I started my comment by saying that this is one way to see religions, a way that I sometime present to curious non-religious friends. There's also a more philosophical (and comprehensive) way to see them that I can discuss with people that are just more "into that". And of course, as a religious person, I do believe in God but that doesn't mean that it needs to be a blind belief without any reasoning.