It kind of defeats the purpose of having singing wars when there are so few people on the list who can sing... Obviously it's all preference, but to not even include in the competition such musicians famous for their voice as Jeff Buckley, Bono, Van Morrison, Madonna, Eddie Vedder, John Lennon, makes this a rather boring comp. I'd even put Nicole Kidman and Ewen McGregor above some of these guys, and they aren't even making their career out of their voices.
Note, Gwyneth Paltrow is an example of why actors should usually keep quiet when it comes to singing, I hope Moulin Rouge doesn't inspire any actors to start bands, Russel Crowe and Keanu Reeves are already too much.