bobby is correct. further, be aware that DD5.1 is the most that TV channels provide and at a lower bit rate than on DVD or Blu-ray, and this is the case for OTA, Cable, and Satellite, and this is the most that that channels provide to MVPDs such as Dish or Cable. Most can not hear the difference, but you probably have a good ear and can hear the lower audio performance fron ANY TV source compared to DVD or Blu-ray.
Now, an OTA or Cable or Sat service may re-encode (they all have to re-encode to send it through their infrastructure to you) the audio to an even LOWER bit rate or further compression (DD is a lossy compression format to begin with) for their effenciency or to keep PQ acceptable, but at the cost of the audio. In general, I find Dish's DD audio to be quite acceptable, but with the pay movie channels such as Starz, etc, sounding clearly superior to the other channels--and the PQ is also superior there, as well.
You are hearing DD from TV channels under-perfom because, in fact, they do under-perform because broadcasters, cable, and sat need to use their limited bandwidth efficiently. And the HD PQ is never as good as Blu-ray because while Blu-ray can average around 30mbps, the best broadcasters can achieve is about 19mbps (most are at far less). The 19mbps broadcast ideal has been adopted by the closed channels (History, USA, etc,) as what they hand-off to cable and sat. So, in general, HDTV is never as good as Blu-ray.