The 'system' call treats its first argument as the command to run and the remaining arguments as arguments to that command. Bypassing the shell means that even if the other arguments contained pipe/redirect characters or other commands, those redirects, commands, etc. will not processed. That helps to eliminate a lot of security problems that can be caused by tainted data.

(Of course, that's not to say that you shouldn't run in taint mode and untaint your data anyway.)

Impossible Robot