I think it's unfair to expect anyone to be completely original. We all take inspiration from others, often without even realising it. Sometimes when I'm walking down the street and I see someone wearing something I like, I'll try and imitate it but put my own unique spin on it at the same time. My style is definitely inspired by others but that doesn't mean it's not my own. I don't wear the exact same thing, I piece together my inspirations.
That's what I feel nearly every celebrity in the world does. No artist, pop star, actress or model is truely 100% original and unique. That's not a bad thing at all. Imitation is the sincerest form of flattery. As long as Madonna or anyone else is not directly ripping off someone and claiming it is entirely their own work, I don't see the problem. For all we know, the celebrities Madonna has been accused of "ripping off" in the past were themselves inspired by random individuals they passed in the street. Unless we all seal ourselves off from the world entirely, there is no way we cannot be inspired by others.
This is all my opinion though, and I could be completely wrong.