I'm pretty amazed by how accepted sampling is. You can cherry pick examples of uses and alterations of original works that are made...better, or at least distinct or unrecognizable. But that's rarely the case. What you usually get are unholy abominations:
http://www.youtube.com/watch?v=vcMfl3UGhOY
http://www.youtube.com/watch?v=uwIGZLjugKA
http://www.youtube.com/watch?v=oROoI-bYgGQ
...I guess it's partly ignorance on the part of the listeners, who don't know the originals, and don't realize how wretchedly they are being used.