All my ATVs are hardwired, not sure what your point is - other than airplay is fat and bloated and doesn't work as well over wifi for many users.
Yes, some of those apps are available directly FROM the device, but thats not airplay now is it... The point is you are normally on a 3rd device and you want to "share" that content to someone be it youtube or anything else and airplay is the vehicle for that. When you do that same task on chomecast it's not using your 3rd device anymore it hands off or "casts" between just the two devices. The approach is different and as a technologist the google way just makes more sense.
A real example. This afternoon, typing on here as it turns out when one of the kids wants to watch the one world show from seaworld,youtube, find the video send the video to the ATV but its still using all three devices and taking up cpu and wifi from my rMBP. Do it on chrome (which i only have one and not in the room i was in at the time) and you cast and the laptop is totally free, its not used at all once the cast is started so no wifi issues regardless of "if" the ATV is hardware (which it is) or not as the airplay is from a wireless laptop. So wireless from the router to the MBP, then wireless back to the router then across a 1Gbe hardwired line from the route to the ATV.
This is why Audio sync is a real problem on airplay.
Play the same clip direct from ATV on the native app and you don't see the same degree of Audio sync issues.
Im not saying buy Google over ATV, I'm simply saying the way cast does its stuff is much better than the way airplay works. It's a protocol 3way.