For any-one who doesn't know of this incident, the a/c span from FL180 and impacted the surface 45 seconds later!
It's been a few months since I read the report but I do remember that this incident was caused by incompetance. It took nearly half an hour from the first ice accretion warning until the final manouvre.
The crew appeared not to take any action and couldn't even make a decision to climb or descend. Now, come on. They just sat in the top of a cloud at FL180 watching the airspeed decrease.
Just applying the correct ATR ice procedure would have avoided this incident.
I can't say I understand your theories as to stall AoA's (rather, I understand them but not their relevance) as the stick shaker values both for normal and icing conditions are well below the values you state.