Who would you add/remove?
Def add John Meyer to the list. (for Celtica)
While his singing skills many not be all that, Meyer can play the hell out of a guitar...
Eh, never heard him play other than that one song that was all over the radio four or five years ago.
Josh Hommes however is a completely different story. He is THE MAN when it comes to guitar.

Everyone on this list is an adequate professional singer, but maybe a bit more successful than their ability would account for.
Some of the most successful singers of all time aren't really great singers, they had something else that made them popular.
TrulyCdn
Not a very well researched list.