Heel striking is a bad thing. You can avoid a large amount of impact stress by wearing cushions on your soles making it less injurious.
But a quick experiment you can try in the comfort of your own home (or just outside). Wearing flats, spikes, or going barefoot, try to heelstrike when putting your foot right underneath you or behind you. Now try a natural heelstrike and watch where your foot actually lands in relation to your body. It will be in front. You've just put the brakes on.
But prove it to yourself. Try to slow down quickly from speed. Your feet will go in front. Try to restrain your pace down a steep hill. Where are your feet? In front.
Try slowing down on a hill with your feet landing below or behind you - tough, isn't it? Takes a huge effort. Pretty analogous to the effort of trying to accelerate or maintain a pace with your feet landing in the braking position all the time.
Elites don't forefoot strike because they are running quick enough, they run quick enough because they forefoot strike (amongst many other things, obviously).
EDIT: I ought to say 'or midfoot strike', just not heel strike.
Edited: 03/10/2012 at 21:31