Johnston,
1) I grew up wearing big shoes just like most of America. I started my running career running in big shoes and in 2001 I was wearing the GRID Hammer.
2) You can re-learn how to meet the ground, although you will have to take your time. I don't know how late in life is too late. The oldest I've worked with in going from trainers to flats was in his 50s and he's healthier and faster now than when I first met him.
3) Footstrikes change. Almost invariably, most runners I've known instinctively move their footstrike forward when they first get into flats. The technique is such that by the time the foot meets the ground it is already in motion for push-off. Later, the footstrike may or may not move back to the heel. My good friend LaWoof, who trains in modified spikes, lands heel first when running at casual speeds. The difference between his heel strike and that of the typical trainers runner is that he does not slam into the gorund, nor does he over-extend.
4) If technique is good there should be no additional impications of stress fractures. Granted, concrete is unnaturally hard and I don't know all the implications of running barefoot on concrete all the time, but one could argue that a few mm's of compressed, firm foam (as found in the forefoot of the H Streets) is essentially taking a piece of soft earth with you, while still allowing for adequate feedback/adaptation with the ground. I would argue that the compressed, firm, thin foam of the H Streets is much more like natural packed earth than standard EVA found in training shoes, with respect to responsiveness.
5) Interesting you bring up football helmets: I've heard a theory that permenant injuries in the NFL have risen because of increased padding. This is because (in theory) a lineman or other player that is sufficiently padded can run head first and full speed into the knees of an opposing player, thereby causing severe damage. Remove the padding ad, as with running, the technique becomes far more cautious and the impact is far less sloppy. I wonder how permenant injuries compare from American Football to rugby.
6) Your sixth point is dead on.