110 channels of MPEG4 HD programming takes less bandwidth than 295 channels of MPEG2 SD programming. I can see the providers charging more for it, but I can't say whether they do or not.
Turbo, according to Dish, died because of contract disputes, not because of customer demands. Scripps Networks doesn't want you to have HGTV and Food Network in HD if you're not also paying for Fine Living and DiY (which aren't available in HD). That's not a verbatim example, because Scripps was actually 100% onboard with TurboHD, but you see the extension. News Corp/Fox and Viacom were actually the big holdouts, and it looks like they won the fight.
That brings me back to an idea I've had for a while now; why are established HD networks like Discovery, Scripps, and others uplinked in SD at all? The 16:9 revolution is well underway, and it's really expensive for them to produce two feeds of more or less the same content. They should be producing and uplinking in HD only, and put the burden of downres'ing on the content on the distribution channels like Dish and Comcast. But if they did that, Dish and Comcast would have a hard time justifying their HD fees.