The reason to buy an apple tv over anything else is the interface and the content, not device flexibility.
There's one more reason for me, and thats the privacy factor. I was told by a Netflix employee that their company can't track the viewing habits of Apple TV subscribers. They know that a paying customer is receiving authorized service, and thats it. If you use a smart tv app, or Android, or a browser window, they can nail down your IP, but not if you're watching over Apple TV.