The law is aimed at straw-purchasers. A straw-purchaser will buy a gun, and then sell it for cash to somebody who cannot buy a gun legally. If the gun is recovered in a crime, and the official purchaser is asked how the gun she bought wound up at a crime scene, she'll just say "Oh, I guess it was stolen".
The law would also be aimed at people who don't give up their guns if government agents arrive to confiscate their guns. "Where are your guns?" "Not here, I guess they were stolen. Bye".
“Where are your guns?” “Not here, I guess they were stolen. Bye”
“Where are your guns?” “At the bottom of the lake. I lost them all in a boating accident, last summer. Bye.”
This is old but good: Gun Registration is Gun Confiscation
An excerpt “If you have reported the gun stolen, and it is then found in your possession, you can be charged with obstruction of justice.”
http://www.freerepublic.com/focus/f-news/2608785/posts