My original thought was that directors of automotive corporations wouldn't want to take a position against other members of their board who might also sit on insurance or pharmaceutical corporation boards. Morton Mintz (of Washington Post/Thalidomide fame) has a pretty detailed take on universal health care support, and mentions this conflict:
<http://www.niemanwatchdog.org/index.cfm?fuseaction=ask_this.view&askthisid=00334>
Speaking of interlocking directorates, I found this while searching around as well:
<http://www.financialweek.com/apps/pbcs.dll/article?AID=/20081116/REG/811129981>
Best, Charles