With all due respect I would say that:
Linux was chosen as the platform for the work because of its growing success and open development environment. Linux provides an excellent opportunity to demonstrate that this functionality can be successful in a mainstream operating system and, at the same time, contribute to the security of a widely used system. A Linux platform also offers an excellent opportunity for this work to receive the widest possible review and perhaps provide the foundation for additional security research by others.
...constitutes if not an endorsement, certian evidence of Linux's legitimacy and utility. No one says that Linux has no flaws or that ndows is the only operating system with flaws. They used Linux because it suited the needs of several of their research projects, was widely available, well know, and as such a good vehicle for distributing their security model -- a model I might add that in theory could be programmed into Windows.