I was trying to get some stats about percentage of Muslims in the English-speaking world (yes, leaving out the odious "rag-head" comment, there are Muslims everywhere) to try to make a case for there being a much higher percentage of Christians than Muslims who speak English (and would be at this site). But the first reputable-seeming site I found with stats points out the difficulty of doing so:
http://www.religioustolerance.org/isl_numb.htm
My overall theory is that a) several of the people you are referring to came here for reasons other than religion and just happen to be Christian/ have an opinion, and in general I've found the people who came here just for religion to be the most fervent and the least skilled at arguing, and b) there have been far more Christian threads than Muslim ones, in terms of Google traffic -- these may turn the tide, which could be interesting.