Satellite providers are not all created equal. DIRECTV and Dish Network both broadcast the signal at different resolutions and it causes a different picture quality. Ever hear of HD-Lite? This is what they are talking about. It is high-def but bit-rate is lower and therefore, a lower picture quality. There is a thread over at AVS Forums that shows you in full resolution the difference in quality. It won't be obvious at first but look at the detail and it will be come evident.
NOTE: expect slow load times for dial-up users due to big pictures.