noglider 

I've worked in a few shops, and in only one of them were we required to adjust all bearings to the right preload, and I mean headset, BB, and wheel cones. The other shops didn't ask us to do it, and when I brought the practice to some others, after having learned it, the owners told me to stop because I was costing them time and there isn't enough reason to invest it, as problems that they prevent are rare enough. That one shop knew that it would have a few customers who ride a lot, and they'd be unhappy if things went wrong. But let's be honest. Most people don't ride many miles. So the word "duty" is a rigid one used that way. There are pluses and minuses to each approach, and it's less a question of right and wrong. I still prefer to adjust bearings, but I don't own a shop.