They also don't support MPEG2 and have told developers (aka Silicondust) that they never will. I agree with you that they want their platform free of any broadcast-related RF tuning ability or video decoding.You may have noticed that they don't offer a DTV tuner so why would they visit Next Gen TV?
I would imagine that Roku places fairly high value on being able to include "channels" from popular streaming services and offering alternatives may raise eyebrows.
Now as for the Amazon Fire stick, I can stream OTA video just fine from an HDHR device. So perhaps Amazon will get on board with 3.0, at least in their Fire TV line.