How do you come to that conclusion? I don't believe anyone has said that. In this particular case (all cases can be different) the OP stated the truck had a issue he KNEW it had a issue some THREE years ago. Sold the truck to a new owner and now he wants the problem corrected. So it should be free of charge? I believe there should be some time frame or a policy on after the sale service!
According to Rob he knew about the coding issue long ago. So ya it should be fixed. Now I think the OP should have handled this better and most likely Rob would have taken care of it. No a tuner shouldn't be responsible for updating a tune forever(unless of course that's part of the original deal), but in a case like this the tune was wrong to begin with regardless of how long it may have take the OP to request a fix.