I think the above comments offer pretty persuasive testimony to support this.
"Way more famous"....wow, that's your "argument"? Seriously?
...or change it to 'Humperdink' and eliminate the argument altogether.
Also, it's like ok if your first thought isn't accepted as the correct answer! You can try other names!
Also never heard of Goulet, but I know all the others. Good quiz. Nice mix of answers.
In any case, it seems reasonable to me that both answers would be considered valid, but perhaps there is some determining criteria I'm not aware of. Quizmaster, is there some reason you feel Willie Nelson is the only correct answer here? Is there some statistic you are using to judge who is more famous?