For my own open source libraries, I have made a conscious decision to say "I don't care". And the language in which I'm saying it is legalese. It's all in the license.
If I felt that people should give me a cut of any commercial software they build on top of my library then I would try to express that in my choice of license.
I have the same view on my own FOSS work (also expressed in its license) and generally also don't think that FOSS authors should feel that their users are obligated to give them anything (beyond the conditions of the license).
Though we as a community can still have views regarding kids hacking things trying to profit off decades of hard work by a large community. Different if they contribute back obvioisly. There are lots of compromise models out there.
If I felt that people should give me a cut of any commercial software they build on top of my library then I would try to express that in my choice of license.