PC Superman barely survived a nuke once, in The Dark Knight Returns. That was no more out of continuity than other pre-1986 feats.
A lightsaber could singe his skin, but it wouldn't cut him open, I would say.
But the reason he doesn't have true invunerability, is his weakness to magic.
The sword & tiara of Wonder Woman have cut him right open (Kingdom Come, Countdown To Infinite Crisis & IC), as have the claws of Vixen & Equus (For Tomorrow), and the black ice axe of Viking (Superman/Batman vs. the Maximums.)
His invunerability is bypassed like it's not even there by these weapons, although DC often tries to show such wounds as surface cuts - except for WW's tiara, which nearly cut his neck in half, and he needed to withdraw from fighting.