I also think that this varies upon location as well. In NYC, they could probably air something much worse and get away with it (unless you're WBAI in the 70s airing a certain Carlin bit), because the community is more liberal-leaning and forgiving as opposed to a station in, say, rural Tennessee, where the community would probably take more exception to any amount of profanity on the radio or TV.
This isn't to say one's right and one's wrong. Radio at its best is a reflection of the community it serves, not that it also shouldn't challenge or push back against something that is wrong. A balance between the two, in my opinion, best.
I still think the profanity rule is absurd and in my opinion a legitimate reason why radio is struggling to some degree. Listen to any Top 40/hip-hop station, the censored versions are downright unlistenable because so much is being lost to the censors. Why would anyone, especially younger folks, listen to some radio disney-fied versions in between commercials, when they can hear the real thing the artist wanted on streaming?
Adults can handle a little bit of swearing. And to the "think of the children!" crowd, one- I guarantee you they've heard and seen FAR worse online and two, there's something really cool called a dial, and you can use it change the station!
Canada doesn't have profanity rules (to my knowledge). In fact, CFZM 740 has that midnight blue show and airs very sexually charged music with full profanity and last time I checked, Canadian society is still perfectly fine.
*steps off my soap box*