GetRandomPercent is a condition function, RandomInt and RandomFloat are papyrus functions.
Ahh, okay, I didn't get what that meant, so I Googled it...
Condition Functions are a set of special functions the Creation Kit can access directly from the game with no scripting. They are usually presented as a drop-down list when adding conditions to an object, as in the example pictured below.
http://www.creationkit.com/Category:Condition_Functions
So basically, GetRandomPercent is used INSIDE the CK, in the "Conditions" drop-down list, where as http://www.creationkit.com/RandomFloat_-_Utility, which is what I use in my scripts for a percentage, is a Papyrus function.
I know this is what you said AstralFire, but I didn't get it at first...