AirPlay (and the competing DLNA/UPnP) have failed on being clear with their messaging on what each device can and can't do. Probably would have helped if each side came up with distinct names for each sub feature. "Yes, it supports PhotoShare, but not VideoShare" or something.

For Apple, they've had "AirTunes" since 2004, and it meant audio streaming to Airport Express units. Over time, they licensed AirTunes to other companies including Yamaha.

In 2010, they added video/photo/mirroring/dual screen to AirTunes, renaming it to "AirPlay". Apple has not licensed the newer part out as far as I'm aware, or if they have it available, no one has picked it up. So for now, only the AppleTV can work for anything beyond audio.