epw
I think you are correct on the TAS thing as well. Your terminal TAS is higher at altitude. So (approx figures here) if say your terminal IAS is perhaps 120 KIAS and you need to decelerate to say 30 KIAS that represents much more than a 90 kts TAS change, an effect amplified the higher you are.
Oxygen and Temperature are obviously survival issues as well, but I'm pretty sure I remember some mention of parachute opening shock as being a reason mentioned, in groundschool, for the function of the Barometric release unit on the Martin Baker seat we were using.
Course, I might be befuddled, It was a while back.
CPB