In the July 9th Chicago Tribune article, "Fewer noses stuck in books,"
the Association of American Publishers claims sale of religious texts
is up.

What defines a religious text?

And, to what do they attribute this increase in sales of religious texts?

I did a Google search for <definition "religious text"> and found this
definition at http://www.hyperdictionary.com/dictionary/religious+text

"Definition: [n]  writing that is venerated for the worship of a deity
 Synonyms: religious writing, sacred text, sacred writing
 See Also: Apocrypha, Avesta, Bhagavad-Gita, Bible, Book, Book of
Mormon, Brahmana, evangel, Good Book, Gospel, Gospels, Hagiographa,
Holy Scripture, Holy Writ, Koran, Laws, Mahabharata, Mahabharatam,
Mahabharatum, mantra, Pentateuch, piece of writing, prayer, Prophets,
psalm, Quran, Samhita, scripture, service book, Talmud, Testament, The
Book of Mormon, Torah, Upanishad, Veda, Word, Word of God, writing,
Writings, written material, Zend-Avesta."

I don't have the statistics, so this is just my opinion (and it's
free!) but I believe that the increase in sales of such publications
has a lot to do with the state of affairs throughout the world, e.g
the war in Iraq, the situation in the Middle East, AIDS, starvation,
corruption and terrorism and the other terrible things we see on the
nightly news. When there seems to be nothing that we can do, I think
many people seek understanding and reason from such texts.

As someone who's familiar with the publishing industry, I would say
that "religious texts" probably refers to the stuff religious
bookstores are selling :)  That may sound overly-simple, but these
sales are NOT included in such ranking systems as The New York Times
Bestseller list...they are considered "apart" from secular works.
(Which is why it's possible to have a religiuous text be a
"bestseller" but not on the NYT list.) Religious bookstores sell
everything from Bibles, the Talmud, etc. to self help books with a
religious slant, to religious fiction.

Kriswrite