I imagine the mechanism is people putting them in the same basket perhaps with other assorted utensils and the water jets simply jostle them all together. They then find the sharpened edge softened by tines, handles and whatnot.
Speaking for myself, I don't put my good knives in the dishwasher for two reasons. First I've had one cut through the plastic basket and get beat up by the spinning whirly-gig underneath and second was me being a bit careless when unloading, and having decided that blade up was better, that left a nice scar on my left index finger. Now I wash, dry and store the sharp knives individually to avoid both problems.
Biting the hand that feeds IT
