My friend got this from Amazon Rep's email: "Only orders placed before September 1, 2008 are eligible for a price difference refund under the Post-Order Price Guarantee policy. As of September 1, 2008 we are no longer offering discounts if prices change on our website after you make a purchase."
Well, it's not like many others would offer this guarantee, so why should they continue with it. I doubt it will affect sales, since people who always want to buy at the cheapest price won't buy from amazon anyway.