thanks for all the interesting answers =D
No I don't honestly believe that we have a different physiology either, I was just listing all the possibilities ^^
One some other forum they said that maybe shang huo are just the symptoms of a weakened immune system in general, and that the qu huo veggies contain valuable minerals ... that seemed to make some sense, although that would then mean that shang huo stuff like oranges is bad for your immune system?
I think the answer has got everything to do with Psychology rather than any strictly biological point. What I mean is; if the human mind is expecting something then it will do its darndest to find it, and Chinese minds have been 'expecting' Shang Huo for centuries.
Or just listen to the Master Chen