> So, just to play the devil's advocate: are NPEs by definition patent trolls? I can't think of a counterargument, but maybe someone else can?
There are lots of counter-examples. E.g. Mojave Aerospace Ventures (MAV): http://en.wikipedia.org/wiki/Mojave_Aerospace_Ventures. It's the patent-holding company that owns all the patents for Spaceship One. It's a vehicle to intermediate between the major investor, Paul Allen, the inventor, Burt Rutan and Scaled Composites, and the various companies that will be commercializing the technology, namely the Virgin Group and any special-purpose joint-venture entities created by it.
MAV (and ARM, mentioned in a sibling comment), is a great example of why NPEs exist.[1] There is a lot of value in being able to take the products of expensive R&D, like the Spaceship One effort that won the X Prize, and being able to package that into a set of property rights owned by a holding company that can transact in those rights. It allows a division of labor that's very hard to achieve otherwise. And division of labor is a good thing, because it allows everyone to focus on their core competency.
For example, in the case of Mojave, you have the separation between the people doing the R&D (Scaled Composites), the people bankrolling the effort (Paul Allen and other investors), and the people doing the commercialization (Virgin, etc). In the case of ARM, you have a separation between the people doing the R&D (ARM), the people making SOCs using the basic cores (NVIDIA, TI, AMD), the people manufacturing the chips (Samsung, TSMC, GF), and the people using the chips in finished products. It's economically valuable to facilitate this sort of separation.
[1] Indeed, MAV is a better example than ARM, because it's purely a holding company. It does neither the research nor the commercialization, but rather exists to facilitate the involvement of the independent investor in the whole process.