Just to add to the complexity of the problem: how big is each square in the game? We can "fudge" the straight vs. diagonal distance somewhat by thinking of the square being much bigger than a ship, and therefore the ship could be anywhere in the square, and some of that "inaccuracy" in position could account for some of the discrepancies between straight distance vs. diagonal distance.
Finally, if hex-based movement systems are that much harder to program, then it might not be as easy as it sounds to account for fractional movement. Not to mention the headaches I'll get trying to decide if I'm in weapons range of the enemy if we try to account for the diagonals. (Although the AI would probably handle it much better, thus giving an apparent increase in AI combat ability, at least until we all get used to a new range system...)
