The Bible has two advantages when it comes to this kind of flim-flam:
1. It's The Bible. That in itself is enough to merit a turn of the head from John Q. Public, whether he happens to be a True Believer or not, and for the Saved, it's especially relevant, since any "hidden messages" in the holy texts can't possibly be simple coincidence.
2. The Bible, like Moby Dick, is an enormous book in terms of the sheer volume of material. Nowadays you can pick up a pocket-sized New Testament from Gideons international, but it's not too difficult to find one of those ginormous, leather-bound coffee table bibles that weighs twenty pounds. When you have that much material to pore through, it's that much more ground you have for your Easter egg hunt, and the greater probability you'll find something "significant". The same could be said for any sizable book, like Don Quixote--recently very popular here at HLP--Crime and Punishment, or anything by Dickens.
If you look around, you can find loads of other fun Bible-based garbage rumors, like how Shakespeare was one of the authors of the King James version, and so on.
Edit: Similarly, Nostradamus's predictions--none of which are valid--are vague to the point that his supporters like to retroactively apply them to notable events in history, like the rise of Hitler or even the 9/11 attacks. For the record, Nostradamus also predicted that the world would end sometime in (May?) of 2000 which, I'm sorry to say, did not come to pass. It's a case of when you're convinced you'll find something, then you will, in a self-fulfilling prophecy.. all it takes is enough time to look over the material.
