> Chromecasts: You can give those to grandmas and they'll just work.

Having tried to train several "grandmas" on streaming media, Roku absolutely trumps chromecast for ease of use. They can understand an on screen interface and a remote. The paradigm shift of using a mobile device or a computer to drive the TV is a pretty big leap. And that is assuming they understand how to use the mobile device itself. That assuming they even have eyes that can see the phone screen, distinguish the very subtle visual elements and the dexterity to tap the little icons.