Your list is definitely many famous voices, but of American music today? Maybe American music yesterday. I'll still agree with 'The King', however I may modernize the list just a tad.
(No particular order)
Elvis Presley
Bob Dylan
Bruce Springsteen
James Taylor
Paul McCartney
I'm not saying these are better voices, or even top favorites of mine (some are), but I think if you're talking about most recognizable voices in music TODAY, I feel these voices would be more recognizable to a larger portion of the general public today.
Regards,
John