@Dream: really, because he is non canon? I was expecting a different answer but I guess I was wrong
@Masterofdeath: That manga's also non-canon since it's a spinoff of a scenario from a video game (Dragon Ball Heroes).
@DBZ_universe: If you try incorporating the anime as proof for feats with this particular matter, then there are other parts to it that contradict the whole "Saiyans can breathe in space" argument like the mentioned near drowning of Goku that I mentioned, Goku wearing a space suit while on his way to Namek and Vegeta also getting nearly drowned when he was getting owned by Frieza.
@Masterofdeath: What manga? I though Battle of the Gods was an anime-only film. The canon-ity of it is still in question if you have trailers showing Gohan going SSJ when he had his Mystic form.
@DBZ_universe: While the environments of space and underwater are different in particular areas, they still share the same aspect: humans (and Saiyans in this case) can't breathe in them due to lack of breathable oxygen. So they are no different in the problems they can cause humanoids without any proper equipment.
And I already mentioned the issues with Goku's moon feat (DB toonforcing) and Broly (consistency issues and lack of presence in canon).