I want to write a bit more on the presentation of real religion in RPGs. Somewhere in here is a meta-commentary about shoot-from-the-hip stream of consciousness blogging of the sort Andy Sullivan maintains, as opposed to a compositional blogging style of the type which, frankly, I more prefer. I leave it to interested parties to unwrap that particular package. I want to talk about God.
Or God in gaming, specifically. I do think that SJG's "Yrth" setting, which must surely have begun as the house game but which first saw print in the Man-to-Man rules and then later was expanded into GURPS Fantasy, was the first significant attempt to portray real-world religions in a manner that was consumed by neither parody nor personal agenda. Religion in Yrth was exactly like religion in reality: messy, complicated, prone to human foibles, and based on faith. I think this last is important; if the gods you worship appear in the city square or fight in battle, that religion is not confronted of the basic question of faith which all mortal religions are faced with. An inhabitant of Greyhawk would be an idiot the claim the gods don't exist. A hero in the Dragonlance setting of Krynn may not believe the gods care, but he'll never doubt they live.
Contrast this with Ars Magica and Pendragon which, while less well-known, is very similar to AM in this degree. In these games, there are mechanics for God. His existence is never in doubt, but the game succeeds in treating the subject in a complex and interesting way because -- while you don't have the question of faith which Yrth had -- you do have a real world religion presented in a "straight" manner which is historically accurate to the source material. I have no idea if Greg Stafford is a Christian or not, or any of the many smart people who have worked on Ars Magica over the years. They could be Scientologists for all I know. That's because the games they have created depict Christianity, Islam, and Judaism in an accurate and faithful way, without polemic or agenda.
The World of Darkness -- at least the original one, which remains the only one I at all know -- did not try to present an accurate picture of modern day religion. Syncretism ran amok, so that every religion was depicted as a colorful but essentially meaningless patina over a central inner truth which all religions shared in common but which no book ever seemed to articulate. The awesome influence of the Byronic hero on Vampire: the Masquerade and its descendants meant that there was a kind of glorification of the "villains" in the Catholic story who, while still evil-with-a-little-e, were mostly misunderstood and tragic. It's not hard to see why this was done; gamers are traditionally pretty secular and the audience for World of Darkness was even more so. These were Goth punks who wanted to sneer at organized religion, not treat it seriously. An opportunity for education may have been hidden here, but it's hard to say. I don't know if I could have, for example, gotten some of the Vampire players I knew to treat a Catholic priest as anything other than a figure for derision.
The best representation of religion in D&D is not, as many will tell you, the Forgotten Realms. While that setting has a myriad of warring gods and story potential galore, religion in the Realms is ultimately more like rooting for your local team than anything which exists in real life. No one asks if these gods exist, they ask who is stronger, who is gonna win the playoffs. Once you pick a team, you're honor bound to stick by that team rain or shine, winning season or losing one. You put a block of cheese on your head in the shape of a moon or seven stars, and cheer your throat raw. It's robust and energetic, but it's not faith.
No, the place to go for an interesting depiction of religion is Eberron, where Baker made the smart decision to put the gods so far off stage that no one knows if they actually exist. There are plenty of big-ass forces which can plop their feet down on Eberron and be seen, but the gods aren't among them. If you believe in a god, that's a leap of faith. And that puts your character at risk. What if you're wrong? And because the alignment of priests, paladins, and worshippers was divorced from the alignment of the faith, the followers of each religion were free to be human again: good, bad, stupid and indifferent.