"Why does everyone think they are owed an insincere apology every time something isn't the exact way they want it to be?"
Because they are the customer that CHOSE your store over every other they could go to to spend their money, that is earned the hard way. Because if they stop coming to you, you lose, not the customer.
An apology whether sincere or merely for face value costs nothing and hurts no one and can go a long way towards keeping customers.
As for Napa it's owned by General Parts Co. and yes they do very well with 1100 stores...but they didnt get that big by making customers angry or not giving them a fair deal.