I have never seen this talked about but I have thought that the bees don't mind our hands and fingers next to them because we are so warm. I often imagine my fingers are just other bees as I am working right amongst them, I could be dead wrong but I sometimes think the bees react to my fingers like they are in fact other bees.
Sometimes bees will fly down and just about light on my hands and then back away, I believe they sense the warmth.
I really believe they accept my fingers next to them as they were bees them selves.
And as long as you don't make any fast, abrupt motions, they seem fine with the intrusion.
Yes, you will get some stings, now and again, you will get a hot hive, that is out of control and just don't want to mind their manners, but most that I deal with, put up with the intrusion nicely.