Chicago has a distinct "oldies" versus "dusties" scene. "Dusties" is a word invented in Chicago (I think some other places use it now) for older R&B tracks that got played on Black radio. The "oldies" station (the main one, which died a few years ago) plays records that got played on a large pop station. It pretty much alternates between a motown type track and a beatles type track. The only "dusties" show now is Herb Kent on Sundays, which is decent, except the music doesn't really change from week-to-week.
I think it's different from city to city. Like in LA there's DJ art laboe (who coined the word "oldies") playing a specific set of oldies that often caters to a specific hispanic audience.
When people say "oldies" on soul source, they mean northern oldies, which could be very rare and obscure records that nobody played in the US (e.g. the salvadors). It shocks me though when people don't know some huge national soul hits (like James Brown "there was a time"). So I don't think it's comparable in the way you are saying, it's not like northern soul listeners have a deeper knowledge of American soul music, it's just that their oldies are different and obscure. Of course, a large percentage of the people here DO have a deeper knowledge of soul music, because they are fans and collectors.