They sold some copies to spankers but they didn't cater to spankers - that's the difference. They kept it mainstream enough to appeal to many different tastes.
Which is easier:
a) writing a magazine that's chocked full of letters about spanking, or
b) writing a magazine that's maybe got a copy of spanking letters in it, along with letters about other things?
Here's a hint - if you go with option B the spankos will still buy your magazine because (at that time) there was just so little mainstream spanking material out there while if you go with option A you might run afoul of obscenity laws.
The Weekly World News was a bit similar - they would have the occasional spanking story in their magazine - and if it got a good response they would run the same article again a few years later. They would change some of the details but the story would be the same.
For example, there are several versions of
http://books.google.ca/books?id=fewDAAAAMBAJ&pg=PA46&lpg=PA46&dq=weekly+world+news+sp ank&source=bl&ots=pU9ovR-tzT&sig=nNH4KelcXyjs7dgIOjaO4-dBblc&hl=en&ei=dml_TtK8BOLZ0QH w1O3sDw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CDgQ6AEwBw#v=onepage&q=weekly%20w orld%20news%20spank&f=false (judge tells husband to spank his wife) and
http://books.google.ca/books?id=D_EDAAAAMBAJ&pg=PT32&lpg=PT32&dq=weekly+world+news+sp ank&source=bl&ots=2xVRkz-ks3&sig=VnfpGuMCiN5YK2iS4ERH8gMzjcg&hl=en&ei=dml_TtK8BOLZ0QH w1O3sDw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBoQ6AEwAA#v=onepage&q=weekly%20w orld%20news%20spank&f=false (child kills a child physiologist who told the child's parents to spank).
Typing "weekly world news spank" into google can bring hours of fun - and show you how they repeated the articles. For example, I said "child" above because the same story has been written about boys and girls (but most times it's a boy) ages 8 to 12. Other than the names, places, dates, and ages it's the same story that pops up again and again - every 18 months or so. As for their advise column, every two or three issues there would a reference to someone getting (or needing to get) spanked. Spanking was only a small part of the Weekly World News, but it got them a few more buyers... Just as those spanking letters got a few more people buying MR.
Goodgulf