Let's also remember that Clark hangs with Wonder Woman, the Black Canary, Zatana, and others. Justice Leaguer Vixen is a a super model when she's not fighting evil. Cat's not even a bench warmer on that team.
According to character writer Jimmy Palmiotti, "Okay. When the character was created, Wally Wood was the artist that drew Power Girl, and he was convinced that the editors were not paying attention to anything he did. So, his inker said "Every issue, I'm going to draw the tits bigger until they notice it. It took about seven or eight issues before anyone was like, "Hey, what's with the tits?" And that's where they stopped. True story."
PG has been retroconned more than most characters, but usually she's a close relative of Supes. I don't think that Big Blue is going to play Sweet Home Alabama no matter how tempting the target.
It was published in a book called 'Dangerous Visions.' back in 1969. It was a collection of all new stories that no publisher or respectable magazine would touch. Some opf the stories are still bleeding edge.