> -- Because you can delete everything on the system with a very short
> command.

This is actually a misconception. 

The very short command doesn't delete everything on the system. The integrity of files which are currently open (including things like the kernel image, executable files for currently-running programs, etc) is protected until they are closed (or the next reboot, whichever is first). These files vanish from the directory structure on the filesystem but can still be accessed by interacting with the running processes which have them open (or /proc/ for the very desperate). 

This is the POSIX alternative to the windows "That file is currently in use" scenario and explains why, when a runaway log file fills up a disk, you have to both delete the log file and restart the service to get the disk back.

cheers
stuart