The vampire is dark, mysterious, and has the looks that can get him laid at anytime. Well at least no in the sun light. But just in those 2 sentences I have summed up the entire series. Why fix something that is bring home the bacon with a fatty pile of cash? Even Stephan King thinks these books are not all that great because there is no change.

What if the vampire could become a human again? what the girl had to move to the other side of the country? what if the vampire launched a war with the humans? What if the girl actually decided to stop saying how much she loves the vamp in every other line? Finally what psychological changes can there be if any of these changes did happen?

Well your not going to get that because the author knows that girls want to keep dreaming about the perfect man/vamp so nothing is going to change.

Where as Harry Potter is nothing short of a modern day epic. There is a plot progression as well as strong and substantial character development.

But harry potter is not in danger simply because its core story line has been concluded, showing that it could attract a much larger audience. It has a much bigger audience because it was able to attract guys and girls. That is just looking at the books themselves. The HP movies will beat out any Tw movie any day for the same reason. In addition, the merchandise for HP will make it untouchable by the Tw franchise.
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This approach “leave it alone” is not new. Look at transformers, madden, and………… well p0%n.

Transformers: good robots vs bad robots. As long as something is getting smashed or blown up it good.

Madden: Every year is the same thing but it just looks better.

P0%n: It really is just the same thing over and over. But guys still watch over and over.

Girls are to Twilight as guys are to p0%n

It is not bad but it does reduce the over all quality of the product from a consumer stand point.