Right. The historical reasons for these laws seems to be because the US is actually 50 competing state economies, and 49 of those states do not contain Detroit.

Right. The historical reasons for these laws seems to be because the US is actually 50 competing state economies, and 49 of those states do not contain Detroit. Dealer protection laws are state protectionism. The fact that states outside California did not go to war to save their local Best Buys when Apple started selling direct, or states other than Washington go to bat for their local Borders bookstores when Amazon appeared (though there has been some rejigging of state sales tax laws around that) suggests that if the same situation were to occur today, in a less regulatory minded era than the early 20th century, states might be less concerned about trying to prevent Michigan car companies from driving their local dealers out of business.