Marilyn Monroe is a old Hollywood Goddess. Marilyn's image was embedded in pop culture on such a scale that, Madonna referencing it is hardly plagiarism, but more so an obvious nod. The Gentlemen Prefer Blondes reference, or the recreation of famous Monroe photoshoots. It's not really the same as popstarlets of today and recent years copying Madonna. Madonna's imagery nods back to old Hollywood, where as popstars today copy Madonna copying old Hollywood
Xtina obviously took from Madonna, with her DIRRTY era, then of course the classic Hollywood imagery for another era... Lady Gaga obviously takes 99% of what she does from Madonna, you don't even have to be aware of their work fully to know that. She works with people who worked with Madonna, the imagery she uses, the songs (Dance in the Dark/Vogue, Born This Way/Express Yourself), the attitude somewhat mimicks Madonna's.... she is aware of it otherwise there wouldn't have been that lie from Gaga's team about Madonna's team emailing her about Born this Way.
The difference between all these starlets today, is that Madonna broke down the door they all walked through. She was sticking up for Gays, using catholic imagery, being an AIDS activist http://www.youtube.com/watch?v=MoikYVj5V6M
, risking her career with SEX, etc... Madonna had guts, and it kind of sucks that they all take the credit, when really all they are doing is rehashing what Madonna did 20 years ago.