I completely agree with your emphasis on the community as one (if not the) defining attribute of what makes open source special. I think, however, that attitudes towards open source in government are definitely starting to shift. Events like the (3rd annual) Open Source Summit [1], and efforts like XDATA contribute greatly to overall awareness of the importance of understanding and embracing open source in government.
As far as supporting established OSS projects, this is definitely a big part of what XDATA is doing. Several of the projects on this list have well-established communities at the Apache Software Foundation (e.g.: OODT, Spark, Shark, Mesos, Tika) and others have strong ties to university research programs (Stanford, University of Washington, USC, UC Berkeley, etc.)
In a sense, what XDATA is doing is helping to connect these communities and funding them to come up with ways to collaboratively leverage their software and skills to solve data-intensive problems.