I think it goes further back than that. You can find early radio broadcasts where the story was brought to you buy some brand. They would even work the brands into the stories sometimes.
> The term "soap opera" originated from radio dramas originally being sponsored by soap manufacturers.
Shows originally brought to you by washing powder manufacturers.
Although I was under the impression that soapies was an American word.
Let's blame Australia.
[1] I've actually been asked, once, "You're English, right?", when I was in the states.
After reading the other replies, I believe that it's not just your part of the US.
I'm going to put this down in the TIL column - I always thought it was American slang, TIL I learned that it's not.
I personally never heard it until this thread. I have heard 'soaps'.