Mac OS X Deleted

hey, i figured out, that you can just drag one of the preset apps in mac os x into the trash......this is pretty weird.....why isnt there some safeguard against it?i mean, if you want to INSTALL an application you have to provide a password....well how come i can just move an app to the trash, just like that?

what happens if say, your roommate decides to be annoying one day?...and if that does happen, and you lose your dvd player, what can you do to get it back???provided the roommate empties the bin afterwards...