I agree, but after a week of 30'-40's, some of them just might want to move forward a bit and someone mentioned that Bocelli has crossed over into pop.
I really wish we knew if there were any limitations to their song choices. Outside of clearance, of course.
I'm pretty certain there are no limitations other than that they must do the week's genre and, of course, must do songs AI has bought the rights to for the week.
They are handed a list/songbook of songs that fit those criteria. Other than that, the choice is entirely the contestant's.