No, I dont think Metallica are responsible for DRM/Protection. They just put a punch into the already developing furor over downloaded music, and perhaps brought a little extra media attention to it.
They've encouraged bootlegging of thier concerts (which only happen once) for years and years, but I can see why they're trying to protect thier back catalog, as thats a seperate entity, and is available commercially.
People were already considering actions against Napster, and Metallica werent the only ones who took on the issue, and Im sure the initial machinations of DRM were already being considered behind locked doors, Metallica just were one of the largest bands to make a stand to protect thier commercially available materials. At the end of the day, they're well entitled to try and protect thier materiél, as Im sure most of us would if we found people were stealing our own personal material. Money is irrelevant, principle isn't.