Your logic is sound. Point 4 is the real argument about what the actual intent of these companies is; The fact that these companies are using the DMCA as a thinly veiled attempt to limit consumer choice and destroy competitive secondary markets. Both of which are repeatedly upheld when legislation or courts take action. Hence the the banning of "Tie in Sales" provisions in warranties on goods.

>Generally, tie-in sales provisions are not allowed. Such a provision would require a purchaser of the warranted product to buy an item or service from a particular company to use with the warranted product in order to be eligible to receive a remedy under the warranty. The following are examples of prohibited tie-in sales provisions.[1]

Regardless of how the DMCA arguments play out, at least the automakers will have difficulties moving forward as there is a long fought battle over not releasing service information on in-car computer and diagnostic information to third-party repair service provides. There hasn't been legislation over the issue because automakers volunteered to release information on service and tools required to service in car computer systems.[2] It would most likely be easy to build a legal case against an auto company that required you to take your warrantied car to a franchised dealership for warrantied replacement of a defective circuit board. So in a not too hard to imagine hypothetical scenario where a bug in the car's cam timing software cause mechanical failure, but the auto manufacturer refuses to sell the replacement part (replacement software) or tools required to perform service to third-party service providers because of software licensing, would that not fall under Magnuson-Moss Act if the repair would be warrantied?

[1]https://www.ftc.gov/tips-advice/business-center/guidance/bus...

[2]http://en.wikipedia.org/wiki/Motor_Vehicle_Owners'_Right_to_...

[edit] spelling/format