You are probably hearing more about religion because the major focus right now is on the South. Researchers have found that 54% in the midwest and 51% of adults in the south attend church regularly compared to 41% in the northeast and 39% in the west (see http://www.barna.org/FlexPage.aspx?Page=Topic&TopicID=10). So there is clearly more attention in those states (Iowa, South Carolina, Michigan, Florida) for religion to be brought into the debate.
It doesn’t help any that Huckabee is very obviously pulling out the evangelical card at every chance. With a candidate running almost exclusively on his record as a Christian-politician, there’s bound to be more chit-chat in the media and on the ground about religion.
Finally, Mitt Romney is a Mormon and is currently leading in the number of delegates (he has almost double McCain’s count: http://www.cnn.com/elections). This is the first time in a long time that a Mormon contender has been taken seriously. In the past Americans typically just wrote off Mormons, but Romney is getting a lot of attention. So the religious atmosphere is certainly different than past election seasons.
I don’t think there are so many Americans thinking only along religious lines. Remember the silent majority rule: the minority is louder because it is the minority. I’ve read a couple polls that have indicated that some people voted along religious lines, but most didn’t. Yes, that’s hearsay on my part, but it’s what I’ve got on the top of my head. Hope this helps answer the question some.