"...if I go to Kriegers or Muscatine Toyota for car service, and the service manager screws me over on a job, I can't hold the dealerships accountable?
You can, but if the service manager was acting independently of the dealership's instruction then the fault would lie with the service manager.
"...If the checkers at Wal-Mart mess up, I can't assume that they had some training from management types?
You can assume whatever you like but that doesn't make it true. If the "management types" trained the cashier correctly then that would be an individual mess-up, no? Besides, what are you doing at Wal-Mart? I thought you didn't shop there.
"...If my waiter totally screws up my order at Applebees, I hold only the waiter responsible, and not the managers who do the training?
You can take it to the manager, but unless you can prove that the manager trained your waiter to specifically screw up your order I think you're barking up the wrong tree.
"...We are to assume that people who work for ACORN get no training, direction or sense of purpose from their superiors?
Nope, however we also can't assume that every action taken by any employee anywhere is at the behest of their employer. People are independent and fully capable of making their own decisions and mistakes.