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I've read that adapter rings for manual lenses in Canon and Nikon might incorporate an Autofocus Confirmation chip...
With my old Pentax K10D all manual Pentax-K lenses had AF confirmation, and they didn't incorporate any kind of electronics AFAIK.
So, why do the Canons and Nikons need that extra chip in the adapter ring?
At least for Olympus and Canon, there is some mechanism disabling the focus computation if no lens are mounted on the body. Now the body recognize that it has an attached lens through the chips.
Based on what I could gather, it appears to provide micro-adjustment, aperture and focal length information to the camera body. The micro adjustment information at least is probably a key portion of the focus confirmation, though I would hazard that satisfactory results could be obtained without the information, if not quite as good.
Most likely the primary reason was to not have to support older lenses. If the feature worked with older lenses, then people would get upset if it didn't support some particular lens. It's easier to simply not have the feature available and if it happens to sell more EF lenses, all the better.
