My house is approx. 50 yrs old. All of the water lines inside the house are copper. I would guess these copper lines are original to the house. However, when you get to say a toilet or a sink, it turns into a galvanized piece. I'm guessing the copper runs right up to the wall, then they used a galvanized piece through the wall. Why would they do this? I replaced some shutoffs recently and noticed the galvanized was quite corroded inside. Most of the house has very strong water pressure, but a couple of the bathroom sinks are quite a bit weaker.
It was ease of installation. They stubbed the copper to each fixture and then installed a plug for testing the lines. After the test, instead of using a piece of copper with a male threaded adapter on it, they screwed a piece of galvanized pipe in. By doing this, they also caused a condition called electrolosis to start. By using two different metals and no di-electric union, the metals have a chemical reaction to each other. This can usually be seen as a white corrosion at the joints.
To restore pressure to the fixtures. Change the nipples to brass with new angle stop valves this should restore the pressure at those fixtures you mentioned. Don't forget to shut off the water at the house shut off valve.
