This seems odd to me -- he is suing the government to ultimately win the right to save them money and give them better capabilities (if spacex isn't better, the government will just stick with united, and might even get a better rate as a result of,competitive pressure). Is it common to file civil suit against the ultimate beneficiary to force them to do something in their own self interest (to the detriment of a third party)?
The related example I can think of was "aerial refueling gate" with the leased aircraft, also involving Boeing.
Government is a special entity to sue. Musk said himself, SpaceX has good relationship with the vast majority of Air Force, it's probably some individual that prevent the process to be more open and competitive.
This is for "national security launches" so they can waiver the competition bid requirements. A single GPS satellite isn't nearly as important as far as "much launch perfectly" compared to a traditional imaging "spy" satellite.
The part Elon Musk is questioning is that they grouped the launches together, so they could hide behind the national security excuse for contract bid requirements, unnecessarily. That and adjusted the time frame so only ULA could possibly bid.
I might be naive, but I don't think his only motivation for revolutionizing space flight is money. He's trying to fix humanity's approach to exploring space, and part of that is introducing competitive pressure.
The related example I can think of was "aerial refueling gate" with the leased aircraft, also involving Boeing.