The word god (small-g) in English is used as a catch all for beings or whatever that have some control over our lives and nature-- but in actuality what "god" is varies greatly from religion to religion (and even that word is dubious in the real world). Until fairly recently in Christianity, as a whole that is, EVERY other "religion" was demonic. The "Mammon" of the bible was a "god" to another neighboring people to the Jews (and I believe some other "demons" of the Bible have similar origins).
In D&D a "god" is something different again from any real world religion-- its a fanatsy world, so they are free to use any definition they want-- the word "demon" or "devil" is also. And I don't believe that Christianity has every differenciated the terms. The words "demon" "arch-devil" or even"god" in this fantasy world are arbitrary will little to do with their real world counterparts.
What I want to say is the terms "demon" and "god" (not big-G God!) have been interchangeble in the past. And if "god" (in D&D or in the real-world for that matter) as some being that has worshipers and has control over us/nature, then I see no problem with bringing any demon to god status. (I don't really see the difference between an "evil god" and a "demon" anyway...). And in this sense I wouldn't have a problem if you refered to Satan as a (small-g!) god.
(As a Christian) I WOULD of course see a problem if WoC or anyone tried to stat God or Christ, or said said demon. And I think I would even if I wasn't Christian. I actually have heard of a d20 Amida-- which I think is going a little far-- and I'm not Buddhist. These are real-world religions. As far as I know nobody worships demons or devils seriously -- even the Church of Satan doesn't actually believe there are real devils.
