I'm not sure there.. the tune is probably their intellectual property, as they have spent the time doing the research and getting it to where it is. To do that from scratch, they'd charge the consumer 10 times as much.
It's probably the same as my industry, we own the code, and the way in which the system is designed. If not, any john cobbly would pay the $x for our system we've build and developed over months and months, and could therefore on-sell that to anybody else they knew, and profit from that many times over. In effect, why go to us at all after that, even though we spent $x getting the system to where it is, and using our knowledge and knowhow.
The logistics of a car ECU tune aren't altogether that different. I have no problems with the policy to be honest, as long as the consumer *knows* this is the case. If they don't like it, they are welcome to go elsewhere.