Amazon.com A9 user discount

Amazon.com A9 user discount -- I was pleasantly surprised to find a discount on an order I placed last night, along with a link to the following explanation:
"Peter O'Kelly, since you've been using A9.com recently, virtually everything at Amazon.com is automatically an additional pi/2% (1.57%) [the original has the pi symbol instead of "pi" but Blogger apparently doesn't like "special" characters"] off for you. Collecting this discount is zero effort on your part. It will be applied automatically at checkout (it will happen whether you use the shopping cart or our 1-Click Shopping®). You don't need to do anything to get this discount except keep using A9.com as your regular search engine.
We don't advertise this additional discount that we give in exchange for using A9.com, so if you want your friends to know about it, please tell them. It is probably the only way they'll find out. All they have to do is use A9.com as their regular search engine. They should make sure they are signed in to A9.com (it should be recognizing them by name) so that we can be certain they get credit for their visit.
While the pi/2% discount is a good additional reason to use A9.com it isn't the best reason. A9.com licenses its web search results from the industry leader Google, and then supplements those results with Amazon's Search Inside the Book™ results. The coolest feature is that A9.com keeps track of your search history for you on the server side. To see how this works, do some A9 searches from your computer at work and then sign in to A9.com from your computer at home.
How can we afford this additional pi/2% discount?
Sponsored links revenue -from the small text-based ads on A9.com and Amazon.com search results pages -will help offset costs we incur through the Rewards promotion. With our automatic pi/2% discount, we are effectively sharing with you some of the money we collect from sponsored links, i.e. sharing the pi.
Please use A9.com and tell your friends."

pi/2% -- clearly the A9 gang is intent on out-nerding Google...