MB,I've been sitting here listening to Bukka White and Blind Willie. You're absolutely right: there are marked similarities between their vocal techniques. Bukka's voice is higher, reedier (and I don't think his guitar technique is as distinctive), but they're an obvious comparison I should have drawn.
What I can't figure out is why Bukka doesn't have an impact on me whereas Blind Willie hits me like that icepick. When I listen to Bukka, I enjoy it but without any real involvement. When I listen to Blind Willie, even now, I involuntarily start to grin. For me -- and I'm the first one to admit these judgments are totally personal and subjective -- Bukka somehow lacks the incredible emotional depth that Blind Willie conveys. Such is the mystery of music.
e