Why do believe in god but not in Zeus or Santa Claus?

I am an Atheist, and I was recently asked by someone what it would take for me to believe in god...so in response I asked them what would it take for them to believe in Zeus or Santa clause...I would really like your guys opinion on this, believers and non-believers. The best argument I get is that because the bible says so, but along time ago the greeks didn't think they were worshiping mythical thing with zeus because they had books about him, there are also books about santa claus, so please don't come back at me with it says in the bible or because the tides go in and the tides go out like Bill "idiot" O'Reilly did.