It's an excellent question; she seems to indicate that they aren't enforced because you'd have to throw _everyone_ in jail. Actually, it's an artifact of the criminal justice system in the US: to speed up many cases with multiple counts, you negotiate some away to focus on the "real" ones. It turns out that the gun laws that are broken are usually broken in conjunction with other, more serious laws. So for instance when a group drives by a street corner and sprays who they think are their enemies, the law about firing a weapon from inside an automobile (a felony) pales in comparisson to the murder or attempted murder charge. That gun charge gets pled. Or the one where the shooter is already a convicted felon and is thus ineligible to possess (yet another felony) seems almost not worth the effort of writing up.
It's paradoxical that so much effort is spent drafting new gun laws when the vast majority of them are impractical to enforce and are typically discarded by the prosecution. When Patrick Purdy took his AK-47 to the Stockton, CA elementary school in 1989 and killed five children (wounding another 29; he fired at least 100 rounds), he would today also be guilty of a law prohibiting possesion of a gun within 1,000 feet of a school. They probably also could have nailed his ass for jaywalking, or expired tags on the stationwagon he set on fire with a home-made bomb (whoops, another felony!).
/jordan