There's something a little circular about your "that's what makes them blues guys" assertion. I've heard a fair amount of blues from "real" blues guys and some of the "technical" stuff you mention was not in the forefront of their playing (fudged notes, poor projection, awkward rhythms, etc.) Were they not realy blues guys? Or was that a function of my cultural ignorance? I'm sniffing some magic supposedly going on here, and not sure I buy it.

What they were playing was blues because they were blues guys who were blues guys because they played it right because..... see what I mean? You seem to be saying that only blues guys can really play the blues, and you can tell it's really the blues because it's being played by blues guys.