Mouse-> This is a reflection of the comics at the time. For instance, in an issue, Supes and Supergirl _flew_ straight across Warworld, tearing it up, but Supergirl was rendered unconscious and the momentum just kept her going, so Superman started flying after across the void of space. He just keep accelerating until, suddenly, the Spectre stops him rather forcefully. The reason? Supergirl had flown so fast she _exited existeance itself_ (!!!). The panel actually showed her flaying out of an infinity sign filled with galaxies! But she was uncoscious, so it would be alright, but Supes was awakened, and therefore couldn't be allowed to _fly_ out of the universe! (The Spectre, otoh, could just pick her up and bring her back... as he did).
In those days, the Flash could even travel through time without the Cosmic Treadmill!