It is reasonable to assume that this is true. But an equally effective way other than making your license unpalatable to them, is just to say no and state clearly: "Patches or GTFO". Also, have a homepage to link with your (hefty?) consulting rates?
I have mentioned this in the past, but there was this weird shift in culture just after 2000 where increasingly open source projects were made to please their users, whether they were corporate or not, and "your project is your CV" became how their maintainers would view their projects. It does not have to be this way and we should (like it seems to be the case with libxml2) maybe try to fix this culture?
