It would add to the feel of certain areas as well. There's already going to be distributable terrain that damages enemies (characters?), so this would be an expansion on that idea.
Perhaps in hot terrain like the desert, your mana/fury/etc meter regenerates slower, as apposed to a steady drop in life. :)
Well my thought on the life dropping areas is that they are either small passageways (like the underground passage in D2), or detours from the primary path whose purpose is entirely MF. That way, you can't just walk in casually. You have to really get focused and turn on your best game before you enter those locations. The best NES games had those levels that everyone struggled to get through, and needed multiple tries. Why shouldn't this?