The point is...
China did not stop them for years after the 1963 treaty ban.
And I probably shouldn't say this without checking first, but France did
above-ground tests after 1963 too I think. And were any of India's above ground?
Please don't think that I think setting off a nuke in Earth orbit is a good
idea. The last few the US did fried a bunch of satellites including Telstar
and created a new artificial radiation belt.
What I find sad about the treaty is that it killed Orion for the US and
any other related projects. We probably could have been to much of
the Sol system by now with Orion.