Good write up in this weekend's Guide from the Guardian about the shite trend of cash in/tag on straight to dvd sequels using the 'brand' name of the successful original but sometimes often not even being much at all to do with the originals. American Pie 7? Lost Boys 3 :The Thirst. A hastily changed script to fit in with the title change can often bring a film that wouldn't see light of day (usually because it's piss poor).
Here's the article
"Sometimes an independent producer will make a movie, and studio marketing guys will see it and go, 'Huh, I'll tell you what, if we name this thing 8mm 2, we can immediately sell 200,000 copies based on that title alone.'"