Gates is just scared. He's one of these new-age ubercapitalists. Profits are more important than people to worthless scum such as they.
The military loves Open Source, for the very reason that it can be easily adapted to new hardware and new roles. They can rest assured of its security, because they can go and look at the code, and then make any improvements they need to. They can develop in-house quickly and easily by incorporating parts of other things, therefore ensuring interoperability.
For someone like them, anything but open source is a bad idea.