thats cool and interesting...but we are drifting....which is ok, just hope we don't get lost

I think my question has been covered. In comparrison, goju has mostly a vertical center of order to do this, goju stances 'tuck in the buttocks' - which in effect, aligns the top and bottom body angles. (straight up and down)

Matsubayashi has a slight tilt forward (hara projection is at a front angle, almost as an invisible 3rd leg)...this no doubt gives a better weight transfer into the target, but maybe at the expense of something else...maybe not. there isn't much linear retreating philosophy in Karate (except with off-balancing), so why not take advantage of that fact.
forward tilt seems like a sound principal, the reason it doesn't look like it makes sense is because I might be looking at it from the logic of sparring principals. When sport sparring, you want to be able to spring in any direction. In self-defense, you need forward and forward angles. Goju is about holding your ground and attacking in place or to the side - let the attacker come into your space. There is an exception in goju and that is the notion of off-balancing an opponent by stepping back and at back angles.

Matsubayashi Ryu might be more 'proactive', hence the hip-tilt towards the line of attack.

In any event, whichever particular flavor and which angle they have you position your hips...there are some principals in all OMA's which hold true reguarding this topic:
* upper and lower torso need to be aligned.
* The 'will' to move originates from your hara. also acts as an invisible 3rd point of gymnastics, this is your center of gravity and centrifigal center when in motion.
* gamaku (driven or rather 'triggered' by hara) controls the speed and force of koshi (hip twist).

I'm thinking out loud...sorry to ramble.