Also the Galaxy Class torpedo launchers were a jack of all trades, designed to fire not only torpedoes but probes as well, to say nothing of being able to burst fire ten torpedoes in one shot. A larger launcher might be needed for such wide and varied loads, but if your just spitting torpedoes like the station was, then a shorter launcher could very well be possible. There might also be an issue or range, considering a longer launch tube might be able to impart more speed upon the torpedo to increase it's range, where as the station might not need such great distances.
Also, if memory serves, the torpedo launchers aboard the Defiant, at least the ones depicted in the the TM, were no where near 20-40 meters long and they were firing Quantums.
That being said, Drexler claims the rotary launchers were Micro Torpedoes launchers: http://drexfiles.wordpress.com/2009/...0%93-weaponry/