This is a perfect example of how today's copyright obsessed culture is holding back technology.
The most practical and economical way to provide a remote DVR service would be for the company to simply record a single copy of everything and retain it for a week or even a month. When a subscriber wanted to watch a show they'd missed, it would simply stream the one copy to whoever wanted it. If a subscriber wanted to "keep" a show longer than that, it could be transferred to their personal storage space. This would use less disk space and would be a hell of a lot easier to keep track of.
But of course, they could never do this because that would be seen as video on demand (which it is) and would require ridiculous license fees, not to mention that half the channels would never go for it, no matter what you paid them.
So instead, they have to have each subscriber tag the shows they want, and record them to their personal storage space. If a subscriber forgets to "record" something, the company has to pretend that it no longer exists, even though there's probably a thousand copies of it sitting in other people's directories.
With today's technology, there's no reason that anyone should ever have to miss a show, regardless of whether they remembered to "record" it or not. The only reason we can't stream anything we want at any time (with the appropriate fees of course) is because of copyrights.
I look at the pirate scene, where you can download almost any show the day it airs, and virtually any movie you've ever heard of, and then I see a cable company setting up a remote DVR that they have to handicap well beyond what the service is actually capable and it just boggles my mind how much the entertainment industry has the technology industry by the balls.
so without copyright obsessed rules it can be just VOD with a lot more shows. But that still does not fix the bandwidth needed to pull this off and comcast does not even have SDV. Cablevision does and even then when they had that free VOD PPV day the system overloaded from the use.