Originally Posted by Jaxon
Kal-El's strength was shown as superior when Zod couldn't free himself from Supes strangle hold at the end. You can see Zod trying to fly up to break it but Supes has the raw power to hold him down. So the 33 years of exposure tips the fight his way.
Also, I get the feeling Zod and co scouted the Earth a little before first contact. You don't just land next to Ma Kent's place flip a trick and have Faora jump 100 feet as a first act of new powers. So it must be assumed they were getting exposure prior to contact (also the scientist on their ship was acutely aware of the powers Kal had gained indicating that the atmosphere would render them useless, which assumes that is what happened to the crew prior).
I'm assuming that they must have come into contact with a Yellow Sun somewhere down their 33 year voyage in space.
I think the difference here though is that they had no real interest in harnessing or keeping their powers like their comic book counterparts or even Donner versions would have since they were all bred in being very focused on their goal, nothing else.