The cases were designed for a lock that would slide into the bottom right of the case, which would lock in place, using a magnet feature. The only way (without breaking it of course) to open it, would be by placing the case on a magnet "key", thus causing the lock to slide out.
I know this because I worked at Blockbuster for a year, and their DVD cases were the same design. Guess Nintendo was being generous with the design so companies wouldn't have to order cases.