It's pretty funny that people tried to steal his tool's name. He even has "testimonials" [3] which I guess is some form of dramatic irony.
I think we should look at FOSS more as we regard math or science. Everybody uses it, but nobody pays for it (edit: once it exists).
It is tricky to figure out how to allocate funds, but software underlies our nation's infrastructure, too. Having federal grants for the maintenance of core open-source infrastructure sure sounds like a cheap investment to me.
One of my favourite scientists of all-time is Harrison Brown. He was most known for his role in launching George Tilton and Clair Patterson's dating-the-Earth project. But he had a most amazing ability to convince the cold-war era US government to fund civilian science that had no real military value whatsoever. He was a kind of science-funding Robin Hood, an ethical con artist.
This might be a bit of a tangent, but the US is still at war and has been (in various stages of "hotness") for many decades). The war in Afghanistan will turn 18 in less than 2 months. More on-topic -- quite a bit of research still gets funding from the military, because of their massive budget (not that I think that this is an overall good thing -- I've heard really worrying stories about the sorts of discussions you have when doing military-funded research).
For instance, it underlies basically all modern science and technology, fundamentally.
Since calculus already exists and is in the public domain, nobody needs to buy it. No government needs to invest money in it. (Assuming that calculus is a finished work for the moment).
This is, of course, not to say that calculus is not valuable.