"Ironically, it often wasn't a prejudice against Christian content that caused most of these novels to be rejected in the general market—the stories simply did not pass the test of great fiction."
I'm not sure I agree with this. Oh, I agree many Christian books are inferior in artisitc quality to secular books, but this is not what kept them out of the secular bookstores. After all, Left Behind has made its way into secular bookstores, and I don't think it passes "the test of great fiction." What it passes is the test of making the almighty dollar. Christian fiction makes money (even if it isn't always great literature), and secular booksellers have finally woken up to that. Stores are big enough to provide that diversity. But has the quality of so-called Christian fiction actually improved since its come out of the Christian bookstores and into the secular bookstores? I don't think it has. Because it isn't the booksellers who set the standard for Christian literature--it's the publishers and what an audience is willing to read.
I don't think evangelical books have a broader appeal than in the past, it is just that today evangelicals are buying them in Borders and Barnes & Noble instead of at a Christian bookstore. There are fewer and fewer Christian bookstores because they cannot compete with the chains, both because of price and because a Christian reads more than Christian books--and it's easier to stop in one place for your literature than go to two. For some reason, it took a little while for secular retailers to acknowledge that there is a very large evangelical population in the U.S., and that these books would mean money. I am surprised at the size of the Christian fiction section in my local Borders/Barnes & Noble, but I shouldn't be. These stores are replacing the Christian bookstores, which will now largely exist for curriculum and gifts, where they exist at all.