I know it's called the Bill and Melinda Gates Foundation, but isn't it Melinda that runs and manages everything? I'm pretty sure Bill just donates to the foundation. I could be wrong tho.
Did you notice the format that report took? Melinda, Bill, Melinda, Bill...
Not that I feel this is the case, but one could argue that having Bill sign his name to something doesn't mean he's not "just a donor" and they're using his name for marketing purposes. Of course, I don't feel this is true, but I wanted to point it out nonetheless :)