Yes, everybody's different. But at least the baseline would be standard and would help. If I sleep 10 degrees colder than someone else, then I can take that info and apply it to any bag rated using the same standard. I mean, your car has MPG ratings for city and highway, but if you're lead footed, none of these will apply; still when shopping for a car it's a good measure of fuel efficiency.
RE: Valandré, I know about them but never think of them; I am sure that if I had started mountaineering while in France rather than here they'd be high on my list. Hey, I could make a chauvinist buy with them :-P.
drC