I always viewed it as "Influence over another entity." Charisma therefore can influence spirits as well, and even the very source of spirits; magic - influence on the Weave.
I had to read up on that ... Magic is made possible by the Weave, which is a manifestation of Mystra, the godess of magic. If the Weave is maintained by a living entity, it does make sense that charisma can be used to exert power of it; creating a fireball is intimidating Mystra.
what about half-elves and halflings?
Maybe that is Mystra taking pity on them because they are only half of something? Thereby offering less resistance to intimidation?
OK, yes, those charisma bonuses are hard to explain.
