Whoa-B said:
When was the first radio edit released? Did radio staffers edit content themselves before someone thought of letting the recording studios do it?
I don't think it ever worked that way. I presume that it's a simple equation - You've made a recording with swearing or offensive content in it. If you want it to be played on daytime radio, you must make a version with that content removed.
Similarly, if you've made a record that's 12 minutes long, you'll have to edit it down to a focus-group-friendly 3 minutes if you want daytime airplay.
Labels are so reliant on radio play, particularly when it comes to hip hop in the U.S., that it's the stations that call the shots. If you don't give them what they need (a radio edit and a handful of cash

) they don't play your record.
Having said that, however, I think the one exception when it comes to the above rule is the chart show. In that scenario, there is more of an obligation for the station to play each record in the rundown.
I certainly recall one record in the UK chart being played and faded out after about 30 seconds, since there was no radio edit. I think perhaps it was
The Man Don't Give A Fuck by Super Furry Animals?
God Save The Queen by the Sex Pistols was also famously "overlooked" when it was at number one.