No, the rest is reinvested to "allow for the continued funding of foundation programs and grant making".
But they do this by "investing for profit".
http://www.latimes.com/news/nationworld/nation/la-na-gatesx07jan07,0,6827615.story
The point is that the focus on maximising ROI inevitably means that ethical considerations come second.
The goal is to keep the foundation around forever so that it can continuously hand out money forever.
Since Bill controls the Foundation, it is effectively he who is handing out the money.
This clearly gives him a great deal of economic and political power.
For example most people have access to investment funds like 401k and such, however, I'm pretty sure nobody really looks at the list of companies or bothers to keep track of the list of companies within each fund.
Unlike most investment funds, the raison d'etre of the Foundation is supposedly humanitarianism.
Given that ROI comes before humanitarianism in 95% of its investments, one cannot help but feel that there is some hypocrisy involved.