Alamak... You mean you didn't know? Here is a link to help you understand.
http://kmp.bdimitrov.de/technology/K-mount/crippled_AF.html
In the older days, there is a mechnical leveller catch on the mount of the body to 'detect' where is the position of the f-stop on the lens. So when you turn the apperture ring on the lenses like FA, M lens, the bodies instantly know what is your f-stop and metering work accordingly. The lack of this feature is known as the crippled Kaf mount. This is the reason why you need to press the green button to stop down the lens for metering on today digital bodies.
I can understand that doing away with the mechnical coupling is to save BOM cost. And today, we use different method of determining the f-stop and metering. So naturally, I don't see how pentax will be bringing back that feature. And it's just my wish. And for pentaxian who love to use manual lens. If pentax ever want to come up with a pro body, they MUST put this back!!!