Yes, given how quickly people are able to flit about the galaxy in spaceships but not even a single hand wave regarding faster than light travel seems to be made, I think it's mostly a case of Sci-Fi Writers Have No Sense of Scale, as usual. The amount of time it takes to get from one planet to another seems to be wholly dependent on how dramatic and tension building it'll be for the most powerful dude (inevitably Goku) not to arrive in time. I assume Toriyama got so sick of it or, more precisely, sick of the nerds in his fanbase complaining at him about it that he simply decided after Namek, "Fuck it, Goku can just teleport now."