It's out there if you open your eyes a bit. There is a TON of microtonality in blues guitar playing - they just don't use the $10 academic words for it.
Well, I'm from a country where lots of folk music is microtonal.
That said, I don't consider the blues guitar playing a major example of microtonic music, $10 words or not. There are some elements, but you can find much more impressive examples in African music for one (part of which could have been inspiration for early gospel/blues musicians).
