Blender obviously has fairly robust support for plug-ins, so why doesn’t it have commercial plug-ins? Blender Cookie put together a pretty slick modeling add-on, but it uses a very open license, and it’s strictly Blender exclusive.
I know the Blender fanboy answer is to say that everything should have open licenses, but people who actually make commercial software don’t often share that idealism. Listening to some discussion about Blender from outside the insular community, a lot of people think GPL code is problematic to work with (which is why Cycles switched to Apache). I’ve also heard some of the developers say that although Blender is open-source, the code base is only understood by a tiny number of individuals, and initiating a new developer would take months of study and training.
I don’t know much about the realities of development and commercial licenses, but what is keeping developers from supporting Blender? Why is it not worth a company’s time to make a port? Is it just that the user base is too small, or is Blender hard to develop for?