If a shop only charged labour and you brought your own parts, they would not be able to survive. The money they make off parts can be a significant part of a shop's income. That is why many shops choose to charge extra labour if you bring your own parts. The funny thing is that alot of times, you can get as competitive of a price from the mechanic or better than if you go out and buy it yourself.
I'm just a crazy m*thrf*cker, livin it up, not givin a f*ck, living life in the fast lane