I've had the same experience. I had a friend that bought a used Powerbook, and he wanted to make sure that it wasn't stolen, so he called Apple with the serial number. They basically said they don't keep track of stolen logs, and that indeed if he brought that computer in for servicing, he would be able to use the remaining Applecare attached to it's serial number.
So I guess this is both a good and bad thing....
*** Shoot films, not guns ***