If the derailleur is adjusted properly that stay damage should never occur; just imagine how much damage would have been done if that chain issue would have occurred on a carbon fiber bike. MTB's and touring bikes (due to the bail or climb out gear) have this issue more then road bikes, but obviously it happens to road bikes as well.
There is a device called a Chain Keeper and other names; but here's what one type looks like:
http://www.amazon.com/N-Gear-Chain-G...4822655&sr=8-4 This device prevents the chain from jumping off the last ring gear and marring the stay.