I see these giant ships as having a foot deep into the door of subspace. It allows them to bend Newton's physics, but not necessarily break them. SFB & SFC 1-3 show this perfectly - big ships accelerate and turn slower than small ones. Speed 0 is stopped. Etc., etc., etc. Even KA had this (with the added bonus of collisions being Newtonian until you regained control, that whole equal and opposite thing...).
One game I played long ago used similar non-Newtonian physics, except when you "cut the engines" - then our old buddy Newton took over and you could coast. Granted, you did eventually slow down (never tried it long enough to see if it would eventually stop or if gravity had any effect, such as crashing into a planet instead of coasting by it). The game was (and I suppose is still) Freelancer.
Just my 2cp.
The Czar