The powers are used pretty inconsistently. Clark has extreme super hearing but even when he's sneaking into the spaceship, and he would logically be extremely cautious both of what's in there and about getting caught, he doesn't hear Lois following him until she makes so much noise that a person with bad hearing would notice her. Superman is so much stronger than Zod that he can break his neck, but he apparently can't just move Zod's head. And so on.
You have to tread very carefully with high powered heroes to not make the powers become plot conveniences that only work when the writer wants them to.
Originally Posted by The Guard
People are overthinking this a bit, though it's fun to think about.
It is still a yellow (younger) sun that powers Superman. His cells absorb its energy in a different way than Krypton's red sun. But, as Jor-El says, "his cells will drink in the solar energy". The film also shows this.
The whole atmosphere thing isn't so much about Superman's powers...it's about Superman's survival, period.
He was born on Krypton, but he did not have time to acclimate to their environment. Most of his life was spent getting used to Earth's environment.
As such, as an adult who had never had to acclimate to Krypton's atmosphere, his body was rejecting the sudden change of being in Krypton's atmosphere. He was essentially dying, or very sick as a result. So he couldn't even stand, or breathe, let alone use his powers.
Think about the way the human body reacts under extreme atmospheric differences. Less air, more water, pressure changes, etc.
This is their backdoor to Kryptonite, and I think it was pretty smartly written.
I'd say that we're overthinking it because I don't think it holds up to scrutiny. Jor-El talks about factors why Kal-El is powerful and he mentions that Earth has a lower gravity. That's irrelevant since his abilities very obviously have nothing to do with gravity. He can accelerate in midair and in space. Gravity is also something you acclimate to and lower gravity makes you much weaker, not stronger, except for a short while when you transition (which means that if anything the other Kryptonians would have been stronger).
That the atmosphere is more nourishing is also questionable. It most consist of basically the same things as on Krypton, otherwise it would be toxic, so what in it could actually be nourishing? And a planet of Krypton's advanced level should have no trouble creating such gas to breathe using masks etc. Superman also seemed to have no trouble being in space, but maybe he would if he stayed there if he needs both atmosphere and radiation?
It works better when you don't think too much about it. While I think they could have gotten rid of some of the explanations, or switched them to something more consistent, I don't expect Superheroes to work with physics.