@nony - I don’t think you can apply the marginal cost revenue distinction to the software industry in my opinion, at least not in a clear cut manner as you could with photocopiers or hard goods.
The reason is that it costs almost nothing to produce a digital good. Seriously, how hard is it to burn an additional CD for the Windows operating system? It costs practically nothing.
So while I think you may have a point about the dangers of monopolies, I don’t think marginal costs would have as much an impact on the software industry, at least from what I can tell.