The sales of Christian fiction on Kindles, Nooks, etc., disproves two theories explaining the popularity of the genre:
1) People buy Christian fiction to be seen reading it.
2) People buy Christian fiction to give it away.
Neither of those hold up with the boom of sales on e-readers. That's not how e-readers work. I'm sure it was still the case that some people did and do buy Christian fiction for those reasons, but they won't work to explain the popularity of the genre.
Both those explanations, incidentally, were predicated on the idea the genre is crap and people wouldn't actually want to, you know, read it.