I have a story for this one. I know a guy with a sporster that did the maintenance himself.
A while later, he found that a battery cable had fried, he took it in to the dealer, the bike is still under warranty mind you... and the dealer told him that since it was something they would have checked and noticed durring the service, they would not cover it under warranty.
He through a fit and talked to some managers,and eventually got it fixed under warranty.
So... its just a real life example.