Question of the Day: What's With the .5 Book Trend?

Lately I have seen so many 3.5, 5.5, 1.5, or just plain .5 books. They don't even called them novellas any more, it's just a small book between books. It's the new trend. I think the first of saw of these was Winter's Passage by Julie Kagawa. This was the 1.5 book between The iron King and The Iron Daughter, but that one I could completely understand. It made sense, it showed the journey back to the Winter Court and it wasn't put on The Iron Daughter cause then the later book would have been too freaking long.

But right now it just seems like something to do, not a necessary thing. Everybody is doing it because, well, everybody is doing it. Some examples of the .5 books:

5.5

3.5

2.5

There are many, many more where these came from.

My question is,

Do you think these books are necessary?

PS;Remember to enter my Good Bye 2011 contest! The Link is on the top, but you can also just click here and it will take you to the post. I have about 40 books to give away, who wants them?!