As far as Christian music: I think when someone sets out to write a song specifically targeted at the Christian market, then it is in the Christian music category. I think when someone writes a song that reflects their outlook on life, and that outlook is a Christian one, then it's just a song written from a Christian outlook on life. (The songs mentioned by Upyerkilt are good examples of this).
As far as there being more Christians, it depends a great deal on what is meant by "Christian." There are more people IDENTIFYING themselves as Christian, but when asked some specific questions about their faith they hold views that are inconsistent with Christian teachings. Some of this is the result of cults (even mainstream cults), some with long-held heresies (for example, I've heard gnosticism is making a comeback), but the majority of which in my opinion is just lazy thinking. An example of the latter is the thought that Christianity is hereditary or genetic somehow. That once is a Christian because his/her parents went to a Christian church or were married by a preacher who spoke about God at the ceremony. I hold a much more narrow view of what it means to be Christian - that one has put their faith in Jesus for the forgiveness of their sins and reconciliation with God. A study not long ago showed that while a high percentage of Americans claimed to be Christian, a much lower number had attended a religious service in the past year, a much lower number than that had actually studied a Bible, and a much lower number than that had a "home church" that supported charitable works with money and manpower. It is easy to call ones-self a Christian, but when it comes to acting like one the results are dramatically different. This is flawed thinking because it is entirely possible to be a Christian and not do the things mentioned in the study as "acting" like a Christian (and vice versa). Nevertheless, there is a very wide gap between the claim and the behaviors one would expect to result if the claim were true.
As far as Muslims, I don't know enough about them to have a well-informed opinion. My study of that religion is extremely rudimentary at this time, though I have several friends who are Muslim and have been kind enough to explain things to me from their religion's perspective when I ask.
You can consider Norman Greenbaum's song anything you like. I don't consider it Christian music, but that is because I define the genre in marketing terms rather than subject matter terms.
As far as R&B, I think the old school R&B folks are being called Soul now, and what used to be called Dance music or Juke music is now being called R&B. It is again about markets and how to sell the music than it is about the music itself. Bobby6string has the right idea. Avoid the lables, except maybe some very traditional ones with definitions related to the music itself (Cape Breton, Zydeco, Highland Reels, Jigs & Hornpipes, etc.) rather than who they want to buy it.
- Zurf
Granted B chord amnesty by King of the Mutants (Long live the king).
If it comes from the heart and you add a few beers... it'll be awesome! - Mekidsmom
When in doubt ... hats. - B.G. Dude