John Law might not count as much (though if he does, Tarantula from Star-Spangled Comics is also on that list), seeing as how the term was common slang for the legal system in general. Finding a John or Johnny Law is like finding an Uncle Sam (also a common character, although only Quality's was ongoing), in many ways.
But yeah, there are many recurring names around the Golden Age. I'd chalk it up to it being a relatively small community (almost all of the writers, artists, and editors lived and worked in the same parts of Manhattan, and many obviously even shared offices) and an understanding that only the top-notch strips become really well-known. Today, I think we're just more sensitive to familiar names and probably have a wider scope. I mean, I doubt readers in the '40s pored over hundreds of comics comparing the strips, whereas that's almost normal behavior, today.