Currently, someone -could- choose to be attractive while charismatic. I don't see anyone saying no to this, unless you want to say "the only reason I have high Charisma is because I'm hot". I'm sure a lot of people play as if Charisma = attractiveness already. The rules in the book exist to prove that this isn't the case, and you can choose to play a non-attractive Charismatic character.
Adding beauty to the equation might those people who already believe that it does to simply double down on their belief, hypothetically.
In other words, the current status quo allows you to play a beautiful high-Charisma person or low-Charisma person if you want, and supports your playing of a unattractive high-Charisma character by the letter of the law.
Changing it might cause people to cite attractiveness as a Charisma trait, and remove high appearance, low-Charisma or low appearance high-Charisma characters as options.
This is further muddied by creatures who would have very different standards of attractiveness, and, of course, races like Elves, who we are told are possessed of such unearthly beauty that it transcends standards of attractiveness.
I see what you're saying, Scott, but I don't see the advantage of the change as it might only impose limitations on the kinds of characters one is allowed to play.
And if an individual DM is annoyed by all the hot pretty PC's of varying Charisma in their game, well, that sounds like a Rule Zero conversation to me.