I always wondered about the "Bookname: A Novel" thing as well. It kind of assumes most books are non-fiction, doesn't it, so when one IS fiction, it's helpful to specify. Except I kind of feel like the majority of books most people encounter ARE novels, so it just seems redundant, and often pretentious, to mention it on the cover. Like "Bookname: My Novel That I Finally Wrote, Ha Ha Mom, I Told You I'd Finish It."
Of course, if it doesn't say "a novel" in the title, and even by looking at the book/reading the description of it, I still can't tell whether it's fiction or not--that's yet another peeve.