Why would I pay for one of the commercial Editions when PostBooks is out there for free? And there's an open source community working on PostBooks. Won't the child surpass the parent at some point?

In all honesty - maybe. That's part of what a software vendor has to get comfortable with in open source, especially if they're pursuing a dual-licensing model like we are. Fundamentally, we believe it will come down to how well we do our jobs managing the PostBooks community. If we're unresponsive, don't give a good sense of overall roadmap and guidance, or needlessly antagonize community members, there's a good chance the project will be "forked" ... and maybe someone will start a PostPostBooks project.

But our hunch is that there's a much bigger interest in expanding PostBooks horizontally - into adjacent markets and with modular add-ins (more on that later!) - than in trying to duplicate the tested and battle-hardened functionality in the commercial Editions.