Given that I can only watch the stream of Cable TV for as long as I subscribe to cable, I would say that I own them much more so than the product I got from Cable TV. If I decide to stop buying new shows, I can still go back and rewatch the old ones as many times as I want. If I stop paying for cable I can't watch anything.
Sure the authentication server could go down permanently, but at this point i've already watched and rewatched most of the shows multiple times over the last 5 years i've been doing this. I've also spent half as much doing this as I would've spent on cable. And I haven't had to deal with commercials.
So far, I also don't see the sun setting on the iTunes store any time in the foreseeable future. If it did, however, I would expect to see a MUCH bigger outcry over the "purchases" people have done on iTunes disappearing. To the extent that it would actually bring the topic up to mainstream news and actually spark some debate and possible change to the laws about what is required to ensure that you can continue to enjoy your purchases in perpetuity. I would also expect people to work much more diligently about then cracking the iTunes DRM.