In the interests of full disclosure, I've never been attacked or eaten by a bear. However, what I've read (Kaniut, Herrero, et al) tends to suggest that black bears will indeed attack humans, but for different reasons than grizzlies typically do. What I recall is that Blacks will attack humans for the same reasons mountain lions do - they're hungry. Grizzlies often start an attack trying to chase a human off (blacks generally run the opposite direction), and when the human is slow or stubborn and gets itself killed in the process, often ends up the mystery meat du jour.
That then lends some clarity to why they say you should fight a black or a mountain lion, but play dead with a grizzly. Somehow, the latter doesn't seem all that wise, either, since the victim often ends up dinner anyway? I think I'll just try to avoid all of them. I don't particularly care for bear or lion filets, truth be known.