Curio: Favorite Singers, Rock Idiom

I scribbled out a list of my favorite "rock" singers quite some time ago, and it has just been sitting around. I don't know what I mean by "rock," except for not Kiri Te Kanawa or Ella Fitzgerald. 

I like their singing better than their music: Sarah McLachlan Ronnie James Dio Paul Rogers Bob Seger Macy Gray 

Their singing makes their music better: Al Green Otis Redding Van Morrison Dusty Springfield Rod Stewart 

"Featured female vocalists": Beth Orton Beth Gibbons Tori Amos Chan Marshall 

Three-in-one: Levon Helm Richard Manuel Rick Danko 

Interesting limitations Tom Waits Bob Dylan 

And then there's Chuck D Frank Sinatra Ella Nina Simone Charlie Rich Emmylou Harris Gillian Welch Kelly Willis Sandy Denny Aretha Franklin Axl Rose Tracy Thorne Marvin Gaye Freddie Mercury