Phil Powers describes watching Dan Culver fall near the bottleneck after summiting K2 in 1993 and attributes his death to not reflexively arresting fast enough (then letting go of his axe). Phil was a long term NOLS instructor (and later director of NOLS) and practiced self-arrest every season, all season long, with beginning mountaineering students so to Phil, his self-arrest skills were well honed and frequently practiced, ensuring they were hard wired into his reflexive muscle memory. He felt that many climbers view self-arrest as a beginner skill and once you learn it, very few continue to practice it on a regular basis. I can say from my own NOLS experience that the instructors drilled into us practicing arrest in a variety of conditions and positions (upside down head first etc), even how to arrest when you've lost your axe. It's a skill that can get rusty if one takes it for granted, and I have been surprised at times while glissading how long it can take in different snow conditions to fully arrest when I've switched over to a self-arrest position.
I'm not saying this was a factor here in this specific accident, after all, he could have had a medical emergency (syncope, heart attack, stroke) that caused his fall. A simple trip on 4th class terrain can be fatal.