These are documented contracts enforced in a court of law, and often very complex and in place for many years. Government has nothing to do with it. It's just a system for active agents in the economy to know where they stand, and know they have recourse if the other side breaks the agreement. Both sides benefit in other words.
Of course in very small companies (say family owned stores) more can be done for cash and on a word of mouth and trust basis. But for large and complex businesses this would never work.
Actually, contract law is a perfect area for Bitcoin to expand into. Read up on Smart Contracts (
http://en.wikipedia.org/wiki/Smart_contract). Because Bitcoins, which are subjectively valuable, can be so easily manipulated at the program level, it's only matter of time before we have easily accessible contract enforcement outside of the traditional state court system (advanced escrows, specialized arbiters, self-enforcing contracts, penal bonds....).
These implementations may occur both at the Bitcoin scripting level or through third-party providers (e.g. ClearCoin). Indeed, the simple act of sending/receiving Bitcoins already represents a simple, self-enforcing smart contract (a transfer of property rights in Bitcoins). Think of how many middlemen (banks, payment processors, government regulators) and costs are cut out just through a bit of Satoshi's code.
I anticipate many businesses (large and small) will start giving strong consideration to adopting the Bitcoin ecosystem when they realize that they can conduct business more predictably and cheaply without inefficient state courts and lawyer overhead.