I don't think the point was that life decisions are being made based on celebrities. I think the point was that someone in a highly visible position was paid/incentivized to use a product and try it out for an extended period of time. After that time/benefit was over Microsoft was hoping she would stay on in because she liked the way windows phone worked. This would show that all they have to do is get the phones into people's hands and then people like them. The fact that she immediately went back to a competitor after the required period was over shows that even after an extended use case people prefer changing from windows phone.
But this also assumes that we can trust 'she only ever had one phone' at any given time. I'm sure she and her rake of helpers / aids had numerous phones / handsets and she was NEVER exclusively using any particular phone. She was just a paid figure head.
I still don't think the VAST majority of general public will give a hoot about this and those that are riding such insignificant news (compared to everything else in the world) have either too much time on their hands or feed their lives through the most shallow of celebrity gossip (does this even constitute celebrity gossip - its so non news worthy?) ....
I mean do we really believe Jay Z only ever uses Samsung phones (didn't Kanye give them both porsche design blackberries), that Alicia Keys really did anything for blackberry or that Robert Downey Jr solely has a HTC ?