OS X dvd helps to 'Repair disk'

Hi, I was slightly shocked to hear that my best pal, who has been using mac longer than me, had no idea that one of the most logical things to do when mac won't boot is to use the OS X DVD at startup. He recovered disk error in 10 minutes thanks to Disk Utility's "Repair Disk" feature avaialble only when booted from DVD (normally it allows to repair permissions there and 'repair disk' is unavailable when not booted from DVD).