they were really only released as three books because no one would publish the book in it's entire piece, cause hey, who's gonna buy a book that big? ;)

it's a reason it's call the Lord of the rings: _________. those are the three parts to the story which at one point was just one entire story. so it can really or should really be called a single movie more over then a trilogy.

The Hobbit is indeed related to LOTR character wise, but it's really just another story. seperated so even if you were going to call the LOTR's a trilogy, you shouldn't count The Hobbit as part of that "trilogy".

Besides, their is no proof that PJ is going to do the hobbit. And frankly, it's pointless to say it wont happen with LOTR's success, but PJ has stated he would like to see someone else do the work instead of him.