One of my favorite topics!! I find that I bend some, slide some sharp and flat some depending on the tune. I agree with all of you that blues guitar is characterized by half tones and expressive slide notes.
As for how these things come to be in blues I really believe that in the hands of some one really into the blues, the guitar will tell you what to play. It'll tell you what to say. Don't believe it? Pick up a guitar you like to play, go in a quiet room and just tune it. While you're tuning up a part of a song will come to you, maybe just a couple of licks. Play it! Develop it, expand on it and experiment with it. That's where the blues comes from.
Don't worry about whether it's modal, tonal, 3ds 4ths 5ths 6ths or half tones or what ever. The blues is from the heart not the head.
Still payin' dues Gene