I was recently speaking to the guy in the mower store about this, husqvarna have some kind of app for your phone, and you have to put a pin code in to re-program it to a new garden. It should be easy to secure the docking/charging station, so thieves would have to buy another one of these.
I guess the thing is that garden tools get stolen from sheds in peoples gardens all the time, so it might be slightly easier to steal a robotic than say a petrol powered mower in a shed, but I am not letting that put me off getting one, I am just waiting for the price of robot mowers to fall a bit before I buy one. Robotic mowers are still a new technology, and I am sure that manufacturers will build more security features into them. They could be securely paired with the base station, so that they can only be re-programmed if the mower is connected to base station that it was bought with, and if you wanted to pair it with a new base station you would need to get a code from the manufacturer.