About the torsion bit, come to think of it, I dont think there is much torsion transmitted to the main hinge during riding. Major force is in plane bending probably.

Or maybe you are pootling along, then the itty bitty front wheel falls and wedges itself into the grating slit of a drain (who the hell aligns grating slit in line with the road!!! ). Before you have the chance to say "what the f...", you slowly tumble to the side while still stuck to your Brooks flyer causing the bike to twist like a pretzel. Hence torsion.

farm4.static.flickr.com/3073/3000698016_a5dd9d021d.jpg

Or perhaps the torsion bit comes when in folded position, bike is thrown by baggage handler down the tarmac. Impact torsion. Oh boy!