Hi foxcom -- I don't find your theory of "prey" tell especially plausible, but I am interested in the phenomenon you describe -- where a mis-hearing makes as much sense (though manybe in a different way) as the original, and so some people become convinced it's the "correct" version. An example of this might be "for all intensive purposes" (instead of "for all intents and purposes"). I've seen these called "eggcorns" (for "acorns"), and "Mondegreens" when they occur in song lyrics. If you're interested, google those terms and you'll find a zillion of them. In fact, I think I'll do that right now to remember some of my favorites.
(The Wikipedia entry on eggcorns lists one that represents, I think, a more likely confusion of "prey" and "pray" than "prey tell" -- "preying mantis" instead of "praying mantis.")