About the saiyans who battled Freeza, they can battle in space but I think Goku is unable to because when an explosion is about to happen in Planet Nemic, Kayosama said that Goku is at a disadvantage because Goku will not survive in space and Freeza would. Again, the flash-back battle between the Saiyans revolution (when Goku escaped), they were all in space, no gravity, no air pressure or whatever, Planet Vegeta in the background...
Also when Goku is chasing Robo Freeza and his dad, he can't Go out of the Pod because he isn't at Earth's atmosphere yet.