I don't know, I've never heard Madonna really belt out a tune. I think there are singers and there are entertainers and very rarely, you'll find someone that is both. I'd classify Lady Gaga as an entertainer and I think it's fair to say you're probably not the audience her handlers are targeting.
I think probably 99% of the people that go on Idol are just singers, Adam hasn't made it so far and gotten all this hype because his vocals are the best that have ever been on idol, it's because he's dramatic, he's an entertainer.
What is Simon going to say to one of those performers that has already made it, it would come off comical since they already have legions of fans. It doesn't mean everyone likes them, just like we both don't like Madonna, but someone obviously enjoys her.