Moving beyond the confines of genre can be a foolish move for musicians. You risk alienating your core followers, irritating your adopted style's diehard fans, and generally looking a fool.
We may live in a time when the boundaries between genres seem more and more permeable (what do terms like Pop, Rock, and Rap even mean anymore?); it may be an era when subcultures have given way to more omnivorous tastes, but how often do you really hear an artist write something radically different?
Swans might write experimental rock, but it's still rock. Kanye West might write avant-garde rap music, but it's still rap.
So, true musical curveballs - when an artist casts off the familiar and attempts something mindbogglingly different - are rare, exotic breeds. But there have been times when musicians stepped well and truly outside of their comfort zone.