I'm defining OTA-exclusive HHs as households that A) watch TV and B) have no subscription to an outside service. I know lots of people who don't own/watch TV for various reasons but I'm not counting them as the DTV switchover means nothing to them. I'm predicting that OTA HHs will be near zero within 10 years as it will require fidgeting with antennas, something that audiences have been conditioned not to do - just like getting up to change the channel. You're right that the effects of the digital transition will take years to sort out and I think very few people will have the patience to wait and see if there's something they or the broadcasters can do to get their locals back OTA. The loss of one station will probably be enough to get people to - maybe grudgingly - get a subscription.
By your definition, I'd qualify as being in an OTA-exclusive household -- I do watch TV, and have no subscription TV services, whatsoever. I watch digital broadcast TV (usually delayed, using a DVR) and supplement what is available off-air with what I can get via the Internet. What I am doing makes a great deal of sense for a certain type of TV viewer -- one who isn't a sports fan, and who is a moderate viewer that is interested in following specific programs. For that kind of TV viewer, the combination of OTA and Internet is an extremely viable option, and one that I believe will become more popular in coming years.
If audiences can get ALL of the channels that they got before without having to do much more than nudge the rabbit ears, than OTA might survive. In Dallas that might be feasible, but I doubt it is the case in very many cities, and certainly not in the exurbs and countryside. Maybe the broadcasters might blanket the area with translators to fill in the gaps, but again, is it worth it at this point considering the demos of those most likely to be relying on OTA reception? Read: elderly, inner city, ethnic, poor, rural, or just plain stubborn.
Another forum that I frequent is dedicated to high definition and home theater buffs -- and you might be surprised to find that the percentage of individuals in that forum who rely on off-air reception for HDTV is approximately 15%. That mirrors the oft-quoted percentage of OTA-only viewers amongst the broader public, which suggests that the stereotype of OTA viewers as being ethnic and poor may not always be accurate.
OTA-only viewership tends to be higher in areas that are relatively flat (like Dallas/Fort Worth or Minneapolis/Saint Paul), and those are also going to be the areas where OTA digital tends to work well. As for whether viewers will be willing to fiddle with an antenna -- the answer is going to be that some will, and many won't. It's like computers -- some folks are willing to go through a lot of hassle to configure their computer exactly the way they want it, while others just want to be able to turn the thing on and send an e-mail. Folks in the former category may be quite willing to fiddle with an attic or rooftop antenna in order to save $50 per month, whereas the folks in the latter group will keep on paying up.
People who can spend four-figures for a true HDTV set almost always have a subscription service hooked to it.
And on this point, I definitely disagree -- there are a significant number of HD viewers who have their televisions hooked to an antenna. In some instances, this is because they bought the set before signficant HD content was available on cable, but in other cases it is because we see the OTA signal as being a better value and/or of better quality.