Cable Card is essentially an "open" tuner. Doesn't have the lockdowns/controls that the Cable Box has. In theory you should be able to take your Cable Card to any provider and it all works the same.
You want your own DVR - so you load it with a Cable Card - and then you switch to WOW from TWC...WOW should treat the Cable Card the same, and all your programs are on YOUR DVR, not the Cable Co's.
Cable Cards had plenty of drawbacks - no VOD, no Interactive PPV, sketchy guides, etc...
When I left TWC some of it was worked out - but some of it still sucked.