this is certainly not true. it would be accurate to say that most reality-tv manufactured artists don't write their own stuff, but its far too cynical--even for me--to hear people say that most modern musicians don't write their own music. current songwriters may not be equal to the caliber of those legendary artists like bob dylan, bruce springsteen, jackson browne, neil young, etc...but an original piece is an original piece, and there are plenty of amazing bands out there writing and recording amazing music. you just won't find many of them on tv, which is a bad place to search for good music anyways.
My main thought is the chances of Supernova writing their own material is probably akin to my chances of winning the lottery ... without buying a ticket.