80% receivers are not complete lower receivers, and CANNOT be used to make a working firearm without further machining. They are just interesting-looking paperweights. The 80% standard is ATF-driven - they claim that anything less than that isn't a gun and can be sold to anyone, anywhere, without records, serial numbers, background checks, etc. More than that, it is a receiver.
Most states allow you to make your own firearms, and you don't need a permit for that, or to put a serial number on the gun. A lot of people who make 80% lowers say that you would be better off putting your own serial number on the gun (a snap if you've got the right equipment and the ability to do the machining on the receiver), just so that it doesn't look suspicious. You aren't supposed to sell such guns/receivers, but I don't know how it'd be proven except if an ATF or state-equivalent agent was part of the transaction.
More and more people are buying these paperweights - and the more that are sold, the less power the government has because it has less information with which to control us mere citizens. More power to this guy, and to all others making them.
So the guys in trouble for following the rules? I know a lot of bureaucrats like that.