As a mechanic, I am dumbfounded by how many people expect you to do minor jobs for free. I will usually do pedal install, minor derailer adjustment etc. on the spot for free, but come on people, my time is worth money. If I chose to charge people for every repair, however small, performed on their bikes, I would totally be within my right.
Not charging money for minor stuff is a way of bringing in future business/service to long time customers. I am almost sure this is a bicycle industry only thing. People wouldn't hink twice about a car mechanic charging for small stuff...