BOTTOM LINE:
I have the 40inch RP model in my basement with NO DISH RECEIVER ATTACHED and it works absolutely fine with whatever I plug into the DVI Input: DVD upconvert player with HDMI/DVI convertor, PC with DVI output (odd resolutin since my video card does not do widescreen, but it works just fine). I used to have a samsung OTA receiver and it worked just fine also.
This TV is only used to watch DVD's now as I am in the middle of a remodel and have no dish receiver hooked up to it. The kids watch their movies on it now for the last month over the DVI connection no problems.