Network appliances are well suited to the task of serving media to multiple workstations, but they aren't necessarily great backup appliances. Media files are generally large and the required data rate for streaming media is relatively low. Consider a 1-hour, 1GB HD movie file. Streaming 1GB over the course of an hour requires only 0.27MB/s. That's a fairly easy task, even over a weak wireless network. If you want to back up 100GB in an hour, and that 100GB is comprised of a million smaller files, that's when you need some more muscle behind the file server.
