The rule they're referencing is actually a pretty good one. It prevents postal workers with an agenda from selectively not delivering non-specifically addressed mail, which includes things like public hearings on land use and taxes, voting information, class action suit notifications, etc.
Unfortunately it's a little easy to exploit, but there's only 1-2 big mail advertisers per region and if you speak to your local post office you can easily opt out of the junkmail they send out.
Does it matter?