I first became aware of the slippage of the idea of a mash-up when I found songs on the iTunes store identified as “mash-ups” which were in fact merely remakes or sample-derived songs.
A mash-up is, as its name implies, a work created by blending two or more existing works. It is not a refashioning of a single existing work, nor is it an existing work altered primarily by adding original material to it.
One can forgive musicians for being imprecise with language, but when the publishing community does it the imprecision tells a different story. It speaks of sloppy thinking, sloppy decision making, and sloppy art.
This recent trend of books that add material to classics — like Pride and Prejudice and Zombies, Sense and Sensibility and Sea Monsters, and now Dick and Jane and Vampires — is not a “mash-up” trend. A literary mash-up would be combining passages from, say, Moby-Dick and The Old Man and the Sea to create a new, derivative work.
Plain and simple, this trend is about sampling and remaking for the purpose of parody.