How 50% Discounts Really Work

Nice, but I don't shop enough to watch the prices and see if that 50% off is really a 10% up and 50% down. I wonder why there isn't a site even remotely comparable to kakaku.com. They monitor prices, show you where deals are, and track the trend. Take a look at this one, for example (just picked off the front page):

http://kakaku.com/item/K0000089891/

Notice all the retailers, retailer reviews, and prices along with the price trend graph at the bottom. Also, users submit reviews of the products. Sure, it's all in Japanese but you can get the gist (or run it through a translator). There are shopping sites here but none nearly as comprehensive as kakaku.