Let me spin you something I've been pondering that I assure you wasn't thought of on obscuro fumes.
Are followes of the God Emperor less theological then the worshippers of Chavs? Here's how I see it. While the Emperor is really just a man and he's had a religion built off of him he still exists. He's alive, sort of, and people have seen him. We know where he lives and we can prove he's still there with the existence of the Astronomicon.
Chaos Worshippers say their gods exist. Yeah there's a hierarchy of daemons, but no one's ever seen a manifestation of a god save the Eldar seeing Slaneesh's birth and they were likely blitzed out of their minds, bodies, and souls at the time so testimonials are sketchy at best. In the end the only thing they can go off of is what they feel, rather than what they can prove. They have to use sorcery and silly rituals with numbers in them to get daemons, not even their gods necessarily in all truth it could be a powerful daemon, to do anything. They work off of pure faith and emotional energy alone.
Humans know the Emperor exists, and is protecthing them as best he can. The more you know it the more powerful you are, and he even rewards his faithful occasionally with very powerful acts that prove he's still intervening in his servants lives.
I'm not sure what the point of that all is, but I figured I'd share what I thought of.