yeah but there wasn't always a Bible. it had to be compiled to begin with by some people. when whatever powers-that-be at the time had determined which scriptures and letters were kept, they left it at that (mostly, anyway).
the main thing, i think, is that they can't add their own scriptures. all the books in the New Testament were written really early AD. imagine looking through a new edition of the Bible that had a book written last year.
julz