I have mixed feelings about this as well, which is the reason that I started this thread.
On one hand, I do think it's a good idea for smaller dogs who live in a space without much if any yard. I also know that in the bigger cities, people are pretty paranoid about letting their dog have access outside when they aren't home (we had a doggie door, but it was in a 0% crime area
). Some people I once knew had a smallish dog and they locked him up in a carrier (no, not a kennel...a CARRIER) all day while they were at work. When they got home and let him out, the poor thing had so much energy stored up he was a hyper idiot for the few hours they were home before they went to bed. What made it more sad is that they had a HUGE back yard with 6' privacy fence and he wasn't more than 2' tall. If they had an option like that, they could at least have put him in a room that was otherwise doggie-proof and let him run around that. And what people said about elderly, ill or recovering dogs really makes sense.
On the other hand, I'm afraid a whole lot of people would see this as a way to never have to walk their dog or take him outside.