Why is i-- faster than i++ in loops?

Question

I've heard this quite a few times. Are JavaScript loops really faster when counting backward? If so, why? I've seen a few test suite examples showing that reversed loops are quicker, but I can't find any explanation as to why!

I'm assuming it's because the loop no longer has to evaluate a property each time it checks to see if it's finished and it just checks against the final numeric value.

I.e.

for (var i = count - 1; i >= 0; i--)
{
  // count is only evaluated once and then the comparison is always on 0.
}