I had emailed Yamaha regarding their OSD implementation. They sent this reply:

In order to have the OSD over lay an HD signal you would need a HD video processor and that would significantly raise the price point at this time. It will probably be implemented in future models when the price of the chips/technology gets lower/better.

I'm not sure what they are talking about regarding an HD video processor considering Tivo S3 can overlay HDTV content with messages, program information, etc... so if a $700 Tivo can do it, why can't a $1600 Yamaha do it?