You can't really say Superman "learned" his powers, the writers just gave him new powers that are a natural consequence of his being in a solar system with a yellow sun. Goku on the other hand had training and instruction from different masters to learn his techniques. As was said, Goku's official story ended with DB GT (as far as I know), meanwhile Superman is continually evolving and gaining new powers as a comic character that gets new writers every few years.