You still are underestimating the cost of Satellites, receivers rolling trucks etc. It isn't just for new installs that is just the more expensive side of it. Existing still needs service, reconditioning at the very least of receivers to replace receivers, rolling for repairs etc. But the big thing you are overlooking is technological advancements. Either Directv is - or is not - going to keep producing or obtaining new receivers. If not they are signalling the end of their use for Satellite TV unless they want to try having someone like TIVO be the source. Either way there is still a cost of doing business involving receivers..New subscribers will need them and expect newer technology as time goes on..
If they intend to keep customers they will be required to keep up technologically and the only way to do that is keep making receivers (or buy them/lease them from a manufacturer) and not just for new accounts, many want the newer equipment when there are advancements.
OTT or eventually wireless will give companies the ability to charge less thus the potential to keep customers or keep them longer, and potentially make as much or more profit.
I do not agree with you that At&t thinks somewhere around 1 million a year, (using your figures again I don't know that is correct) ten million over ten years etc just for satellites is a drop in the bucket when they have the means to provide TV other ways with much less cost outlay.
Remember I don't think At&t planned for getting out of the satellite service soon, the question is if pushed to make a decision as they may now be is Satellite more important than owning content.
The current hardware can't cost them much to make. Probably less than $200 for the HS17, and clients are definitely under $50. The main things that break in DVRs historically have been power supplies (so now they are external) fans (now they don't have them) and hard drives (not much you can do about that)
Sure, they will keep producing receivers. And keep charging people $7/month for each TV - that's $84/yr or $420 over five years. Five years is the depreciable life they use for their receivers, so the receivers are MORE than paid for by the fees they collect even if you just have HS17 + one client, with a little extra left over for refurbishment if a customer leaves - and the more TVs you have the more profitable those TV fees become, adding $420 in revenue for $50 of cost! Probably the only repair they do now is replacing a failed hard drive - if the electronics fail on an HS17 (let alone a client) it isn't feasible to repair, so if it won't work with a known good power supply and hard drive they'll just recycle it.
People might "want" new equipment, but Directv has historically not handed it out just because something new was available - when the HR44 came out, they didn't let people upgrade to it from the HR34, there are still people with HR21s, and so on. But newer equipment doesn't make much difference now - HS17s and C61s are pretty fast, while newer servers might support more 4K TVs at once, and newer 4K clients might support 4Kp120 eventually there isn't much "new technology" that's coming. If they didn't upgrade customers just because they wanted it back when HR21s totally sucked, they sure aren't going to do it today.
It will be interesting to see how the pricing for the IP delivered version of 'full' Directv will work. Will they still charge you $7/month per TV, charge by stream, or will they try to get rid of the separate fees and simplify pricing? They will still be providing equipment to these customers, so if you think providing equipment is expensive they aren't getting away from that cost (except for the 'server' unit) by switching to IP delivery.