I also think it a bit odd. It is the same as our 3 so I have gotten used to it.
#beacuseracecar (drive)
The pattern really does come from race cars in regards to the direction of G's a driver experiences while driving. It applies a bit more to cars with sequential transmissions, where the shift pattern is just up or down vs the standard manual shift gate pattern.
When accelerating, you're being pulled into the back of your seat, so it takes less effort to also pull backwards to upshift in the same direction. When braking/decelerating, you are being pushed out of your seat, forwards towards the front of the car, which is also when a driver would be downshifting. So it is easier for the driver to push the gear lever forwards in the same direction he's being pushed. If it was switched the other way around, you'd be working against the forces that are being applied onto you in order to change gears.
Manufactures are struggling to find a standard for this. It's a balance between "racing" logic and "conventional" logic (shift up is up, down is down) and what they think their customers would want. I read somewhere that the standard Mitsubishi Lancer's automatic manual mode is in the "conventional" layout, but in EVO trim, it's in the "racing" layout. So even on the same car, it's different, mostly because the customers for a standard Lancer and Lancer EVO are pretty different.
I had a Dodge Stratus that the manual mode was side to side. Toward you was up shift and away was down. Leave it to Dodge I guess.
Your explanation seems logical enough, but it's also conflicting. You say the shift pattern goes along with G forces, yet race cars ("racing" logic) have + up, - down.
so Porsche gave paddle shifters. I'd be happy with that.
And the whole side to side shift pattern in dodge actually came from Mercedes, when they were financially tied together. Some Chryslers were also fitted with the side to side pattern due to that relationship.