These companies have to reduce churn, but also have to be able to attract new customers. I don't think new customers rate thinigs like DVRS before makning their choices, they choose on the channels they can get that they want. A new customer stays with its provider for a long time, so this is a critical juncture to attract the first time HDTV buyer. The present customer (as you say correctly) probably does NOT have HDTV so they spend less, the new customers will probably have HDTV and thus spend more.
No doubt not having the most HD hurts for new customer aquisitions. How much it hurts is not clear. It must hurt enough for them to give free HD DVRs.
The ideal provider would have the most HD, the cheapest prices, no commitments and free equipment and installation. Each provider values (or is forced to work around) various parts of this formula.
DIRECTV: currently most HD, likely to stay number 1 or tie for the next couple of years (they probably will have more capacity than Dish for a couple years, but Dish may be able to put up every available HD channel when their satellites go up, making it a tie). 2 year commitment, $$ for HD DVRs.
Dish: 2nd in most markets for HD. Has a good chance to catch up in HD channels, 18 month commitment (24 month next month), free DVR.
Cable: usually 3rd in HD, depends on markets some can match DIRECTV (like fios could). Short/no commitment, free equipment.
Costs are all up in the air. Since every cable company charges differently and even DIRECTV/Dish vary by a lot based on what equipment you have (DVR fees, # tuners, etc) that it is very hard to compare.
A blanket post like the first one in this thread saying Dish is going under not being able to offer a few HD channels is just hype. Dish is still the best solution for a segment of the market, DIRECTV has their segment and Cable has theirs. Many people may go to Dish over DIRECTV when they see the cost of HD up front (HD DVR lease upfront fees).
I personally am not under commitment with Dish, but I refuse to go to DIRECTV since there is no way to get DIRECTV HD without a 2 year commitment. Dish has done a better job servicing what I value. Yes I would love to see more HD on Dish, but I rather watch SciFi in standard definition for a few months to save a few hundred dollars (2 HD DVRs) and a 2 year commitment. If the cable company picked up more HD and had SciFi I might consider going there. I personally view the market as way too fluid for a 2 year commitment and I really hate the way the DBS market is moving to longer and longer.