What do you mean by 'uncoupled' then?
It's sort of the same, SC just does it differently. SC keeps ship stability active (spin etc) but carries the movement of the ship, if that makes sense. So when flying uncoupled you keep going in the direction of movement, but can freely rotate the ship but the ship rotation self-stabilises - and to change your direction of movement you manually control the thruster. It's kind of awkward to explain if you've not tried it.. but I find it allows for a greater degree of precision control by manipulating the momentum of the ship feathering the throttle.
Disabling flight assist (from a quick test) appears to allow me to carry the direction of movement while rotating the ship (without auto stabilisation which is a bitch) but you can't manipulate the momentum in the same way... *shrug* I'll try it more in depth tomorrow.