The Living Tribunal1 said:
well the upper atmosphere has only a few molecules per square cc
compare that to billions on the ground....
Needing very little oxygen is still not the same as needing no oxygen, though. Goku got to fill his lungs full of sea-level oxygen before going into the upper atmosphere. He didn't start the fight there and just begin breathing. Besides, as I already said, Goku himself confirmed he was in danger of drowning, and Beerus wasn't really doing
anything besides just holding him, down there.