The arrangement of songs is a big part of what makes something good, though, and can be considered an original work by itself. You could re-sequence a movie and release it as a Final Cut, and it's still a movie. You could compile original material that was never officially released, and you could take tracks that you've used before in one studio release and include it in another one. What matters isn't that all the material is original, what matters is whether or not it works as a cohesive and interesting piece in isolation, IMO.
What makes compilations undeserving of being on these lists, for me, is that they're usually just thoughtlessly thrown together and never sound like a cohesive experience. For instances when they do, though, I see no reason to get caught up in the semantics and labels. If it works, it works.
