Treebore
First Post
I generally think of level as having the most to do with life force (which relates strongly to HP and barely at all with Con). Attacks based around snuffing out someone's life tend to bypass HP (Finger of Death/necromancy effects, Enervation/level drain). So then XP in the sense of 'fractions of a level' would also relate strongly to life force.
Actually HP has the most to do with your "life force" in terms of how things typically work. Take your Finger of Death example, What happens when you make your save? You lose HP's. Not XP's. What happens when you lose levels? You also lose HP's, including CON bonus', which directly modify HP's.
So I can see how people can link strength to level, but I see a much stronger link to HP and their CON bonus, or penalty.