No, I am not assuming. I am reading that only 20% of homes have DVR's and those that do in fact DVR a program say the program is "not essential" viewing (as per Nielsen website) and the urgency to watch the program is not there.
The DVR numbers reflect
actual viewings of the recorded programs...that's why they take 7 days to calculate. They count people who watch the recorded episode within 7 days of broadcast. The numbers say that Dollhouse viewings increase 30% when those are factored in. Those aren't potential viewings, but real ones. It doesn't matter how many homes have DVR's... just how many people are recording the show and watching it.
If the ratings drop so far that all of the show's advertisers pull out, then downloads alone will not save the show. However, high download numbers plus high DVR numbers mean the show can survive significantly lower night-of-broadcast ratings than it could have even 5 years ago.
I don't think that after the "Firefly" debacle, either Fox or Joss would have bothered with this show, in this timeslot, unless they were thinking outside the box in terms of profit sources. Why pour $30 million into producing a season of a series that's guaranteed to fail right from opening day?
This is a "proof of concept" show.... that's why they put it on in a timeslot that, under the old models, would be suicidal. Fox wants to see if they can make a profit on a show with low-to-mediocre Nielsens, based on new media paradigms (DVR+Download+DVD).
If the show continues to lose half a million viewers every week, then it's all moot. But Fox knows they can't remain successful as a network in this economy by holding desperately on to outdated models.
Of course, Joss himself is looking even further ahead. He wants to do shows that are only made available for download and DVD, like Dr. Horrible (A very successful proof-of-concept experiment in its own right.)