I may be able to shed some light on her 'popularity'
Madonna first came to light in the early/mid 80's she had a certain appeal to a section of the record buying public in the way a certain Ms Spears did about 15 years later
At the time the record industry were looking for the next new thing, punk had died out, new romantics were showing signs of ageing and were no longer 'new' and there was a general dilution of the pop scene, at the time we had 'soft rock' 'metal/thrash' 'rockabilly' and 'mass produced' pop had just started as well as a number of other generes.
Madonna was something different, yes she was very controversal, her outfits were different to the point of getting her into trouble, but this was her way of getting known, and remaining in the public eye, even if people are talking about you in a bad way they know who you are.
Because of her rebellious nature she attracted kids who could relate to her, hence the start of her fanbase, over the years she has 'matured' with them and whilst she has lost fans along the way she has also pick many more up due to her constantly changing musical taste.
I like her in the 80's and went to see her in her True Blue tour, for me that was her at her best, from there i went off her music, but she has always courted controversy, her book 'SEX' was another classic example of that.....i have one of the metal bound copies and even today it is resque!! like a prayer with a black christ, her kissing Britney Spears live on stage.....it all gains her publicity
American pie she mullered, i agree, but then i have never like that song anyway.
Her talent is her ability to understand where the music is heading and either pulling it in that direction, adapting to it or creating her own style, and for that i believe tshe has earned the right to stay where she has been for the last 20 years....
Her personal life should remain that.....and in my view her religeous beliefs should not be something she discusses and tries to encourage others to adpot....again that's my view.......
And remember we are talking about her, have you ever thought this was orchestrated so as to keep her at the top of the media pile?