It's not only about looks, but also about acting.Maybe the picture that goers with that article was not a good choice to begin with.
A bit OT but did anyone here see the movie "Beyond the Sea"? Kevin Spacey did an incredible job of portraying Bobby Darin. I had no idea he could sing that well either.
I think Johnny Depp could pull off Dean Martin, not Sinatra though. The only actor that comes to mind that might pull off Sinatra is Harry Connick Jr., who would obviously have no trouble with any musical numbers.