I think that the initial question was "why a 0 resistance compared to a ridicously low resistance". And my point is that it's easier to get a superconductor than some material with "ridicously low" resistance. As you said, silver is unusable for potent magnets, and such is any other non-superconducting magnets.
Probably if we had materials with a billionth of the resistance of silver they would work, but we haven't. And we have superconductors, luckly. :)
Probably if we had materials with a billionth of the resistance of silver they would work, but we haven't. And we have superconductors, luckly. :)