The issue becomes when things are developed with a mix of public and private money. I'm not saying we shouldn't tackle the issue, only that it can't be as simple as public money = public resource. If that were true, nearly all of us would be required to work for free, since we got the majority of our education through public funding.
Edit: It seems everyone ignored the generalization I was replying to. Yes, in terms of code it's actually relatively easy to require that a publicity funded project be open source and leave it at that. The business can decide if they want to write everything from scratch to protect their IP or if they want to open up existing code as a part of fulfilling/winning the contact.
In terms of other partially government funded projects, like the pharmaceutical example given, it's much more difficult to say how much of the process and result are thanks to public funding. That's really the only point I was trying to make, that it can get very hard to draw the line. With code, it can be relatively easy.