Yes it is baffling since the HR10-250 has been doing it for a long time.
Well it is not baffling to me. I am a software developer so I know what issues can arise with developing code. The reason that the OTA tuners are not there is because then the box is just like the R15 (two tuners) All the logic for recording is the same. That way all you have to focus on is adding the HD capability into the system.
When you add the OTA, you now have a total of 4 tuners. Plus some of them are not interchangeable with each other. Plus you can only support 2 record streams and 1 play stream on the Hard drive and you can see that this is a much more complex the operating environment.
So I can see why they would want to get the box out there without the OTA to validate the robustness of that part of the system. By holding back, they have been able to eliminate many bugs in the main part of the system without the added complexities of the OTA environment.