There are actually "shared source" cars. New Jaguars have standard Ford parts (source), Lexus and Toyota share many of the same parts. Going even further, look at Disk-Brakes as a module, nearly every car built uses that module, they may have tweaked the module for thier own uses, but essentially most of the "source" is the same. Many vehicles also use the same licenced patents, more shared "source" :)

"Nothing is sure but death and taxes" I say combine the two and its death to all taxes!