@Cerberus. Please feel free to add your own answer. I'm in a hotel with a very wobbly Internet connection (the swimming pool is much better). And I don't manage to check my facts. I'd be very interested in your take on that interesting question in any case.
I've undeleted my answer and left open a number of points. If anyone can throw in precision I'll be most grateful.
Many scholars (JSBangs, Kosmonaut) being away, I'd be even more grateful.