The word bible is derived from the Latin biblia and the Greek biblion, both meaning "book". Nothing sacrilegious about it, etymologically speaking.

The Bible, therefore, is "The Book" and when capitalized refers to the authoritative Christian religious book. When not capitalized, it just means a book that is considered definitive or authoritative on a given subject (either by its readers or, more often, its publisher). "The _____ Bible" is recapitalized only because it's used as a book title.