I know a large number of YC companies, and only a minority fit that description.

Being charismatic isn't entirely unrelated to one's ability to lead a company. You don't have to be slick, but projecting enough charm that people don't wander off while you're talking helps with hiring and sales.

You can learn to be acceptably charismatic if you put some effort into it. If Bill Gates and Jan Koum did it, you can too.