Lots of people implicitly expects them to be working in the long run. Lots of people will read a tutorial on how to get the cool animation X and the tutorial will only include the -webkit-property, and the reader won't even bother that he is excluding a big part of the users, because he uses only a webkit browser, so he won't notice.

There is something inherently wrong with vendor prefixes as they are used currently. But in the same time they are good if some browser wants to implement a new alpha feature or something.. but they should really not be supported for so much time as they are now.