The US Gov't doesn't always act like a single buyer. The contracts people talk about are like that, but most of what the DoD does is a much smaller scale.

Work for a company with lots of small contracts and you'll quickly see "oh the Navy does things this way, AFSOC wants it that way, DHS does it another way" and so on. Competition arises among the small companies because all these different agencies behave like independent buyers, even if they are all part of the same government.

The corruption issue is damped within the realm of small contracts, because it's hard for executive-level corruption to trickle that far down the bureaucracy. It's just hard to make a bunch of smaller organizations move in lockstep, even if they have the same top-level leadership.

Granted, network effects still matter. Certain groups want their stuff to be compatible with other groups' stuff. They all talk to each other too. If you bin a demo with JSOC and the guy has a buddy in AFSOC, you bet he's gonna get a beer with his friend and say "man, company X really binned it today." So there are still some consolidating pressures.

And you're right, all of this falls apart with the huge contracts. Just food for thought.