As long as we're on the subject of invulnerability and kryptonite, I was wondering...
It seems to me everything and everyone from Krypton is invulnerable except for Kryptonite, which over the years has been pulverized, liquified, atomized into a sprayable gas, cut into jewelry and bullets and all sorts of other things by various Earth-dwellers.
Why is it, then, that Kryptonite doesn't possess the same properties of super-toughness that everything else from Krypton does?
I believe that whatever made it turn into Kryptonite, changed it's properties so much that it lost its invulnerability. Kryptonite didn't exist on Krypton, it was just rock that was changed into Kryptonite when Krypton exploded and thus changing its properties into deadly Kryptonite, this process also no longer made it invulnerable.