Whistle, I'm not sure I understand. Are you arguing that mixing minors into major progressions is a defining characteristic of blues? If so, I have to take exception. I know bunches of blues songs that have narry a minor in sight, relying entirely on majors and sevenths. On the other hand I know bunches of songs — folk and otherwise — that use minors extensively in major progressions. Many songs in C major use relative minors — Am, Em, Dm. What am I missing in your argument?
And Barky, hundreds of blues songs are anything but slow tempoed. Some are, but I don't think it's useful as a defining characteristic.