Yeah - in a world of magic and weave, Charisma is also an expression of your ability to impose your force of self on the world around you, to a certain extent, especially for caster that use the stat for that; and yeah, that's personal and usually emotional... Justifying it as a racial bonus is... odd. It makes more sense, in that light, for tieflings than others, since if you look at it in this particular light, tieflings have a supernatural edge from their heritage that literally makes it easier for them to impose their will on the world around them... but if that's the angle you take... what about half-elves and halflings? You've got to interpret it differently for them. So, yeah, it's a bit of an odd duck.
