No, Jeff, it is NOT commercial software, and may not legally be made commercial (in the sense of closed source and limited distribution). Twiggi is based on TWIG, which is a GPL'd package, and therefore must be GPL'd itself. Darrell may, if he chooses, only distribute it commercially (that is, only to people who pay him), but he may not legally prevent others from distributing it freely.
Of course, if you pay him, he does provide support, and I'm sure he does a very good job of that.