That's the thing. Always take the drive with you when you leave the house, just in case there is an earthquake or a fire. That way you have off-site storage with no additional expense.
... and, you have your movie/music library with you. Want to watch a movie, no prob! Want a copy? We can do that too! Drag *N* Drop!
Hasn't anyone seen the Seagate commercials?
..OK, here's a bone. Just develop an backup drive that's built into your car with wireless access. It's part of your network when you are at home, then when you are away you can either connect to it wired with your laptop or connect ad hoc wireless. When you leave your house in your car, the backup goes with you. Not a solution for everyone, but it would work for many. Now all of you engineers out there get to work on it and make your millions.