Couldn't agree more. That's one of the reasons the manufacturers are fighting so hard to retain all their 'proprietary data' within their own systems. It forces people to get a new vehicle and the tradein value is close to zero unless the 'manufacturer's dealers' offer something. It's awfully close to deceptive practises, in some ways. Some years ago, the Ford Tempo (I think it was the 85 or 86 model year) would bring up the engine warning at 30,000 miles, because Ford had decided that the EGR valve should be changed then (nothing in the manual about it though). Of course, the majority of people took their cars in because they thought they had a serious problem, instead of a non-issue.
After getting a lot of complaints and 'investigated' by the FTC, Ford 'offered' to fix the issue (and refund money) and not just put the engine warning light on simply to get people to go into their dealerships (and spend money) for no actual reason.
It'll be a while, but perhaps we'll see the various controllers in vehicles become commodities - maybe, maybe not.
Cheers
PeteS