People who are looking for more power to do video and picture editing, an bit of extra performance for AAA games. Of course, you may end up buying one in the future as more games get coded to use more threads within your processor.
Server cpus, however, are a different branch altogether. They have ECC and are built for stability over performance. The higher-end server processors can also be teamed on a single motherboard so the given higher performance on databases and well threaded applications. They're not restricted to servers, they're also used in high-end workstations.