How come Marilyn Monroe is celebrated as a plus sized icon?

I've seen hundreds of pages devoted to celebrating Marilyn Monroe's famed figure.... but many of them make the claim that Monroe was plus sized, and they celebrate her for having the guts to be a fat sex symbol. But, Ms Monroe's measurements were a teensy tiny 36-23-37, and at her heaviest (while pregnant, nontheless) was 140. She was never plus sized, always extremely thin. The claim that she was a size twelve even is a tweaked fact. A 2012 size 4 is equal to a 1950s size 12. She was always extremely thin and graceful, but somtimes even looked emaciated. Why do people insist on calling her plus sized? I'm not prejudiced against plus sized girls, I love them, but Marilyn wasn't one. Do people not understand the difference between curvy and plus sized? I simply don't get it...