Well, at least life-forms from Krypton can be assumed to have evolved the same kind of ability to absorb Solar Radiation that the people of Krypton did. Of course, they would probably develop entirely different abilities then just copying Superman's powers.. Perhaps Kryptonian plants just grow at an incredible rate?
On various occasions, notably in SUPERMAN RED/SUPERMAN BLUE, the seeds from the Scarlet Jungle have been caused by Earth's Yellow Sun to grow at incredible rates of speed, their leaves becoming as invulnerable as steel under those conditions. It is unknown if they could manifest other abilities, but really the point is moot when it comes to them: they're PLANTS. They can't have superspeed because they can't move, or supervision because they can't see, superhearing because they can't hear, superbreath because they don't breathe, and super-shout, because they have no voices.
Krypto and Beppo and the Super-Gorilla, all animals from Krypton, has manifested identical powers to Superman - which means that ALL animal life on Krypton, not just upright, bipedal Kryptonians, become "Super" when exposed to Yellow Sun Rays. In fact, knowing what we know about the laws of evolution and the similarity of vertebrate life, it would be strange if we had to explain why Kryptonians are the only form of life on that world that would have powers.
Elliot S! Maggin posited the theory of the Photonucleic Effect, kept on this site incidentally, which is impressive and uses lots of big, big words and is as good an explanation as any other, I suppose. From a guy that "gets" Superman. There's also Mark Wolverton's SCIENCE OF SUPERMAN, which has a few very well-thought out theories of how Superman's powers work: namely that the reason the Yellow Sun/Red Sun thing makes a difference is because all life on Krypton has a type of supplementary system, sort of like chlorophyll in plants, that allow them to make energy from sunlight.
Like I said earlier in this thread, I don't know if I'd agree with the sentiment that Superman's costume not being "Super" should be something that should survive the next big revision. Mostly because I think a super-costume is neat! I love how his cape is super-stretchy (elastic enough to, for instance, stretch over to catch all the flood level rains falling on a small town like a giant circus tent) and has a pocket for his Clark Kent clothes, and how (at least Supergirl's) has tele-crystals on the belt that tell her the time both on Earth and in Kandor.
Allow me to revise my statement: I would support the concept of Superman's costume having an origin other than the Silver Age concept of it being indestructible under a yellow sun - provided an explanation of equal interest could be supplied, and the outfit had properties that were just as mindblowing.
Here's a few that are just a "for instance," to help you know what I'm talking about:
Superman can change his costume instantly, because the cloth atoms are stored in a can on his person in the form of "dust," and rubbing his hands together at superspeed to create static electricity would cause the costume to "form" on him.
Superman acquired his costume by capturng a pair of creatures on a distant world that are sort of like earthly silkworms, except the "silk" they produce is the hardest substance in the universe, sort of like weaveable versions of "unbreakable diamond filaments" from Arthur C. Clarke. Superman's costume has properties depending on the mood of the space-silkworms when they made it; for instance, if they were cranky and the Superman Robots didn't feed them enough, the costume would start changing color psychadelically.
Superman's costume isn't a physical object at all, but is instead a variety of solidified thought: think of it like a "three dimensional thought photograph." This accounts for the reason the costume is indestructible: as it is solid thought, it doesn't really exist at all.
