I'd like to take a moment to dedicate this post to the bustiest of all mainstream superhero comic superheroines , POWER GIRL!!!
Here are some excerpts from Wikipidia and from an interview with Amanda Conner, Power Girl artist, who explains how PG's boobs got this big!!!
Physical appearance and costumes
Power Girl's original Wally Wood artwork showed her as relatively busty but otherwise her figure and build conformed in appearance to other contemporary comic book women.
Power Girl was at one time portrayed as having a highly athletic but slender physique. Artist Alex Ross restored Power Girl's extremely busty shape in the limited series Kingdom Come, rendering her as a heavily muscled Power Woman (as if an ardent bodybuilder). This approach has been carried forward by most other artists. Power Girl is consistently depicted as a curvaceous young woman, and her physique is one of her most recognizable attributes — to the extent that various writers have acknowledged it in both serious and humorous ways.
For example, Justice League Europe #37 attempts to explain Power Girl's revealing costume by having Crimson Fox question her about it; she receives the reply that the costume "shows what I am: female, healthy, and strong. If men want to degrade themselves by staring and drooling and tripping over themselves, that's their problem, I'm not going to apologize for it."
Conversely, in JSA: Classified #2 (written by Geoff Johns), Power Girl explains her cleavage-window to Superman, revealing that "the first time I made this costume, I wanted to have a symbol, like you. I just… I couldn’t think of anything. I thought eventually, I’d figure it out. And close the hole. But I haven’t." At the same time, however, the issue highlights the humorous element when a man who Power Girl has rescued is so fixated upon her chest that he doesn't even look her in the eye to thank her. A similar treatment of the character can be seen in Superman/Batman #4 (written by Jeph Loeb), in which the heroes need to distract the Toyman while Batman and Superman battle Captain Marvel and Hawkman. Seeking a way to accomplish this task, Batman notes that their opponent is a thirteen-year-old boy, and all attention goes to Power Girl, prompting her response: "What's everyone looking at me for? How am I supposed to distract... oh."
The character's costume design has varied greatly over the years. Her classic costume design from All-Star Comics #58 is that which is in use today - a red cape and belt, blue gloves and boots, and a white bodysuit sporting a cleavage-exposing window on her chest (its variable size and shape determined by the artist depicting her). During her time with Justice League Europe/America it transitioned to a capeless yellow and white bodysuit, followed by a blue and white costume with a short mini-cape, headband, with a diamond shaped opening on her chest. She has also worn a headband, as had Supergirl prior to her death in Crisis on Infinite Earths. In a guest appearance in Green Lantern, Kara is seen in her large wardrobe closet with every costume design she has ever worn in DC continuity, deciding which costume to wear for that mission. Her original costume returned when Geoff Johns had her rejoin the JSA.
FROM AMANDA CONNER INTERVIEW
In convention appearances, Conner said that, in drawing the arc, she’d be channeling her inner Wally Wood, referencing the comics master who’d handled Power Girl in many memorable stories, and helped give the character her look back in the days of the All-Star Comics, when she debuted in issue #58.
Clarifying her comment a little, Conner said that finding her inner Wally is adapting her style in a certain manner.
“It’s all in the boobs,” Conner said, laughing. “I’m not too great at mimicking the styles of other artists, but I know that Wally Wood was a boob man. Adam Hughes told me a story he’d heard about Wally Wood doing Power Girl. The legend goes this way: Wally said that in each issue, he was gonna make Power Girl’s boobies slightly larger than in the last issue, until the editors catch him. I think he made it all the way up to his 11th issue before the editors said, HEY!!! NOW CUT THAT OUT AND BEHAVE! I’d love to take a close look at those eleven issues and see what went on with that.”
“In her first appearances, her outfit seemed relatively tame, although Wally did have the circle cut out at first,” Conner said. “I’ve never had a chance to read all the things she appeared in, so I’m not sure at what exact point it became the hot bombshell costume, but some women are just extremely comfortable with their bodies, and don’t mind showing off the parts that they’re proud of. And as it’s been mentioned before, it does provide a great distraction for those that would cause her trouble. Power Girl isn’t too sure of what’s going on inside of her right now, but the one thing she can be sure of is that killer bod of hers. She might as well run with it. I’ve only had one person express concern about her body and her costume, and I explained that’s just the way the character is. I also mentioned that I draw each character differently, ‘cause just like real people, they’re all not going to look the same. If you look at Saturn Girl, she is much more slender and wiry than Power Girl. Power Girl is Power Girl.”
As for more on the look: “Actually, there is a scene in #2 where she explains her costume, so I won’t tell you. I’ll let you read it. Although in my circus of a brain, I don’t know if it has any other meaning than ‘WOW! Nice ones! … and thanks for lettin’ them breathe!’”