To those asking the question "why aren't patents automatically in the public domain?", the question received a decent answer on Stack Exchange two years ago:
"No, they are owned by the U.S. and controlled by the specific agency where the inventing happened. However, there is a policy of licensing. It is covered in 35 USC 209. The logic behind this is that the U.S. would like the public to benefit from the invention and if anybody can do it, it may very well be that no one actually does it. Without some exclusivity it may be that no one will be able to justify the investment to enter the market." -George White
One of the comments to that answer also suggests inventors of government patents also get a fixed percentage of revenue, which wouldn't surprise me as an incentive to drive government employees to come up with novel inventions on the clock.
http://patents.stackexchange.com/questions/9994/are-patents-...
"No, they are owned by the U.S. and controlled by the specific agency where the inventing happened. However, there is a policy of licensing. It is covered in 35 USC 209. The logic behind this is that the U.S. would like the public to benefit from the invention and if anybody can do it, it may very well be that no one actually does it. Without some exclusivity it may be that no one will be able to justify the investment to enter the market." -George White
One of the comments to that answer also suggests inventors of government patents also get a fixed percentage of revenue, which wouldn't surprise me as an incentive to drive government employees to come up with novel inventions on the clock.