First off the big networks that are leaving analog
C-band are going to digital C-band, though many are using DCII megapipe (not compatible with 4dtv) or they are using SA's power vu there is no consumer unit that can sub to these feeds.
Channels that have left analog or the older type DCII that the 4dtv can't get, NPS and SRL have made a deal with a company called HITS
http://www.hits.com/ they supply rural cable co's and use the older DCII tech like our 4dtv's do, so this is why you have channels on 4dtv Ku-band on Galaxy-4, since we can't get the master feeds anymore.
A good quality DVB receiver on a good quality channel will look better or the same as a 4dtv channel, some feeds look much better, other feeds that can't be seen with any dvb receiver on the market in the usa look better than a dvd, the
HD feeds also blow away ota and 4dtv HD, many feeds are on both c/ku band.
C-band is still the freq that most broadcaster use, many raw feeds and smaller broadcasters use Ku-band, or a mix of both, there are also a few big nets using ku to distibute there feeds.
If you have a big dish c/ku 4dtv and a slved dvb receiver are the best combo you can have.
Maybe sometime in the next year or two big dish users will be able to get programming from
http://www.auroras.tv/index-home.html NPS is working on a deal with them.