Oh, dearie me.
What a sad, sad state of events, Steve. I'm so sorry for your fall, and a truly Big one at that. I was hoping for something of a lesser sort when you mentioned it so casually, but this was a step Beyond. I hope everything will soon feel better, and I'm sure we're all grateful it wasn't worse for you. As the old saying goes, "So long as you can still walk away...". Well, I think walking on crutches after an Air-ambulance ride still qualifies it as a better day than it could easily have been. Thank goodness it wasn't worse.
<nods> Yes, I think this was one of those unhappy occasions where everything aligned just right (wrong) to make it possible. A person thinks "If only..." in retrospect, but you've done us all a great service in listing the factors, any of which could have easily done the deed, and so are worth keeping in mind.
Amidst your pain and misery, it seems almost crass to ask, "Is the bike okay?" Hoping it wasn't hurt too bad in the carnage.
All the best,
Dan. ("Speedy Recovery" your way...)