Totally agree with you. This can be said of many greats. Gary Moore and Brian May first come to mind. A great singer would have significantly enhanced their music (and possibly appeal, but that is less important as long as the music is great).

I personally would never have thought that these two (Beth/Joe) would mix well. They were made for each other. Brilliant. That will not make me fall in love with Bonamassa's playing otherwise though. I have a few of his CDs and they are good, but I can think of many players with a better balance between great vocals / guitar playing. His voice doesn't do it for me on a full album. I also do not think that Glenn Hughes was the right fit. Judging from his collaboration with Jimmy Barnes and Beth Hart, bluesier vocalists, with "raspy" / rough voices seem to gel well with his playing.