I've noticed that the sudoers file and cron config files act in a special way compared to other config files on Linux. They need to be edited with a special wrapper rather than any text editor. Why is this?
You use visudo mostly to prevent from breaking your system. Visudo runs checks on your changes to make sure you didn't mess anything up. If you did mess something up, you could completely wreck your ability to fix it or do anything requiring privileges without rebooting into a rescue mode.
The man page describes this.
Zoredache answer is perfect.
One more thing that can be worth to mention. You can use you favorite editor by setting