Oh please,determination,dynamism,etcetera don't have nothing to do with this.This is about publicity and marketing techniques.'Global Ambassador' is just a fancy name to cover this up.They just need a pretty face with succes and a little bit of 'je ne sais quois' to promote their products.
Most people that are not-informed of features, or don't are about features usually follow what someone else is doing. This is marketing, and it's why you see celebrities using blackberries or the latest motorola phone.
Now people that know features (like us) will buy based on what the phone does, not who carries it.