and those that do are generally the ones who realise they need to put the effort in and develop their talents!
But the necessary talent isn't really singing or songwriting, it's self-promotion. Madonna, Kylie, Robbie - they're not exactly known for their great voices. The voice and songs only need to be *just* good enough that it doesn't stop the product selling.
Madonna's got to be the smartest operator around. Good luck finding a Madonna record that's pushing any boundaries musically. They sold because she's made a career by using her body as a promotional vehicle. The songs themselves are pretty much disposable commodities from hired hands, and whether they're good or not is almost immaterial.
Nothing new about this, of course. Buddy Holly was no great shakes musically, but he was white so he could be sold to the white record-buying public.