Reason behind tubing/ pipes from refrigerators going as number 2 or anything but number 1 is that often times it is a special alloy copper. We make a couple of specialty alloys here (copper/brass plant I work for) that are considered air conditioner/refrigerant copper. Basically so things are added to make the copper more flexible and I belive to work better with refrigerant chemicals.
I know it caused a serious headache when someone here screwed up and ran a roofing/structural copper bar in place of the refrigerant copper. We caught it just before it shipped out the door.