I don't know for certain if the below is the only difference, nor am I sure how it relates to package installation, but here's my crack at it:

In OSX, root is the same as almost all other Unix systems. Administrator is almost as good. In OSX, an Administrator is in the admin group, which allows them to run "sudo", to run commands as root.

Now, knowing the little I do know about OSX, I do know root is not enabled by default. Administrator is. Depending on the administrator scripts, you may be able to require admin privelages, and sudo your commands.

Either way, they'll be prompted for either an admin, or the root, login. My gut instinct would tell me to go with administration requirements, not root.