Well everyone obviously has their idols and role models, but that doesn't mean she's copying Madonna, or trying to become famous off of what Madonna has done. There are, obviously, strong comparisons between the two (glamorous, rock-ish, rebel image, BLONDE,) but in my opinon, that's it. And any similarities between the two wouldn't exist of Stefani wasn't blonde...regardless, of the mentioned similarites, I feel they are all just coincidental and not malicious. Did Madonna ever have a clothing line? And Madonna was never in a band.
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson