Nah, Amazon's pretty accurate on it's sale prices; it's the "before sale" prices that sucked. In anticipation for the DeepDiscount 25% off sale, I had made an Excel Spreadsheet to compare the price differences between what I'll be spending at a DD during the sale as opposed to what I would have spent at Amazon.
Last week, for example, the Shakugan no Shana box set was being sold at Amazon for $62.99. Now that sale has it at $38.99. It's still not as cheap as the price DD will be selling it for during the sale, $35.43, but it is definitely discounted from what Amazon had it as last week. Of the nine anime I have on my list, seven dropped in price for this sale, one stayed the same, and one is no longer listed at Amazon at all.