AFAIK, OS-X processes run as the (nonprivileged) user, and only during software installation and system changes are user actions run as root. HAL implementations and things allow user interactions, such as a user being able to execute a dialup operation or to mount media. When a system update or a new piece of software is to be installed, or a system setting such as en/disabling a service, a dialog asks for the user's permission. Most better linux distros do this through sudo or it's guified variants. I almost NEVER am asked for permission to do something because I almost never make changes to the SYSTEM.
To play devils advocate, the same may be said for Fista, but Fista asks permission for EVERYTHING!! The user is so often annoyed by the stupid mother%$#@%%^# UAC bull%$#% that they no longer pay attention to whats going on requiring a priv elevation and just click (I agree)(I agree)(I agree)(I agree)WTF!?(I agree)(I agree)Leamme alone willya(I agree)(I agree)STFU i keel you(I agree)(I agree)(I agree)AGGGGGHHHHHHH THE %$#@!?(I agree)[DOOMSDAY] %&^%% NO CARRIER
That implementation is a recipe for disaster. I actually ship all Fista installs with UAC Off because it does no good anyway, plus, most remote control implementations don't work for %$%# under it.
Now, anything prior to Winders Fista, it's practically a hard REQUIREMENT to run as admin. Even something as harmless as Acrobat Reader will not run well without God privileges.