Wysocki,
It just sounds like an incompatibility between the Sanyo and the Dish to me. My Sharp M20x assumes that any 1080i or 720p input is 16x9 material, so 4x3 material shows up in what most people call bordered mode (bars on all sides). Now your Sanyo sounds like it does the same thing, except that they have added a special mode in 720p to allow you to do the 4x3 full screen. I would then expect (as you indicate) that 16x9 material would get cut off at the sides. Sounds like the Dish 6000 isn't built to handle that special mode that Sanyo added. Unless this mode is a generally accepted way of doing things I wouldn't expect the dish to know about it. The 6000 is just putting 16x9 or 4x3 out as 720p without modification and the Sanyo is blowing it up. I don't even know how the 6000 could handle this without making some lines blank (and losing resolution) in the 720p signal. Seems like a pretty specialized mode that really only applies to 1024x768 projectors.
Seems that as we move forward receivers, DVD players, and projectors will do a better job of integrating all this stuff, but at this point different assumptions seem to be made in different places. I don't think sending your receiver back is going to do you any good. Disclaimer: I don't have one - I'm just speculating.
--Darin