Hi Seth,
Good question. The security group named Security Administrator is
just a name, you can easily rename it to Administrator, Super User,
Omnipotent, etc. To change the name, click Setup / Security /
Security Groups. Then click the EDIT pencil (or just click on the
Security Administrator group name) to get into edit mode. Change the
name and press SUBMIT.
The Security Admin checkbox on the User screen is used to give a few
additional rights. For example, someone with that checked can go to
Setup / System Configuration / System Options and change some global
settings that affect all users (like whether to allow rich text
editing, etc). They can also setup email alerts for other users.
Hope that helps.
Steve