The "older generation" does not use metaphors because they are limited in their thinking. They do it to illustrate the principles underlying law. A basic principle of private property is that you don't have to secure it. The burden is on the would-be trespasser to figure out what rights she has with respect to the property and act accordingly. Snooping around private property out of "curiosity" is illegal, whether or not there are locks preventing you from doing so. (This is an idea teenagers have had trouble with long before the Internet, but we manage to beat it out of them every generation).

Those principles apply equally well to the Internet. Ordinary law-abiding people don't go fiddling with URLs, just like law-abiding people don't jiggle door handles or peak into windows to satisfy their curiosity.