I'm going to bullshit my way through this.
1) The Kyrptonite was inside of the planet, so they were not exposed to it.
2) Photosynthesis. He retained the energy of the sun and made like a tree.
3) What..? They are posers, obviously.
1) If Kryptonite kills kryptonians, and kryptonite is made of the planet Krypton, How did the kryptonians last as long as they did?
2) If Supermans powers come from our suns radiation, how can he do battle underground, or in bunkers, or in his radiation-proof suit.
3) Why is Superman the last son of Krypton, when his cousin, his dog, his relatives, and a whole city survived?
You obviously know your Superman facts.
He's superman. Nobody knows what the fuck is going on with him, because he is retconned every ten minutes.
1) There is some conflict that Kryptonite kills all Kryptons. It, for example, doesn't seem to be lethal to Kara Zor-El. Readers have also been led to believe that Kryptonite has such a dramatic effect on Kryptonians only when they've stored large amounts of energy from a yellow sun. (IE: When they've been on Earth a while.)
Likewise, there are other types of Kryptonite, not just the green rock so many automatically associate the term with. Why? Presumably because Krypton, like Earth, is made up of more than one kind of rock. Safe bet, in fact. So certain kinds of rock in Krypton's geological makeup are dangerous when exposed to a Kryptonian charged with the energy of a yellow sun.
Not unlike when humans are in danger when exposed to rare natural elements in certain conditions. The odds of such a danger coming to pass aren't all that high...except when it's the only thing your enemies have found to stop you. (Such as Superman's case. Although magic is also a big weakness for Big Blue.)
2) Superman, like any Kryptonian, is a living battery. They gather and store the energy of yellow suns. So why can he do battle even when away from the sun for a bit? 'Cause, he's a battery. Literally. He can and has run out of 'juice.'
3) Media hype. Another plausible answer; he was the first, and not only that but he was the first and only Kryptonian bopping about for a while. And clearly the only one running around being all Super, until some of the others started to make their own mark. Also, Kandor is still relatively a secret. So you really can't count that. And while you can point to a few female Kryptonians, Superman is really the only Kryptonian male in the limelight. So of course he gets the 'Last Son' billing.
Hope that helps!
"Though we live on the US dollar, you and me got our own sense of time."
Order of the (spacey) Advanced Roleplayer
I think someone just like to go over problems.
Jesus, Ruby. You are Sharp.