So, if you bought a DVD licensed by Sony, can they now legally enter your house and take your DVD?
No. You fully own the DVD. However if there are any features that are live based they have full rights to deactivate those. You can (grey area) legally make a backup copy of said disc. However, it's also (grey area) not legal to break encryption (which almost every disc has) to make said copy, so catch 22. (Someone I'm sure will correct me if I'm wrong). But since it's for personal use they haven't really pressured that.
There is no "license" with a DVD. You bought it, you own it. It's just the law that you can't make copies, sell or distribute them, or I believe show it to your neighborhood. (Legally I don't even think a bbq movie night with more than 5 people watching is okay, which is why Microsoft reeeeally loved the whole kinect camera watching you)
Sidenote, this post makes me so sad. People have become so accustomed to renting everything we have to explain what owning things was like. "What, you mean you could just have it? And they couldn't come take it away?"