MyWifeSays - 11:01 am on Mar 9, 2003 (gmt 0)

I would imagine you are dealing with an algorithm that gives a score of how likely it is that the domain is being used by a new owner. Content change would probably be part of the algo.

Registration details, DNS server and site ip address and time offline would probably be taken into account too.

The algo. isn't going to get it right all the time but as long as they err. on the cautious side it should be a big improvement.