Amazon has been targeting customers for many years just based upon past buying habits established at their website. Advertising from Amazon, via both the website and automated email, is based upon your product selections in the past. This has a side effect of reinforcing your future product choices to be consistent with what you've bought in the past, which can be restrictive in your future buying choices. I buy most of my books these days in e-form for Kindle. If I happen to have selected science fiction or technical books in the past, I'm besieged with suggestions for further books in those categories - to the exclusion of genres like history or biography. Netflix does the same sort of thing with its movie suggestions. Amazon, Google, Netflix, and the like are at least up front about their personally directed advertising policies. The worst thing about this data harvesting revelation with regard to Apple app developers is that it is happening without revealing such policies at the outset. One way some apps get around this is to bury any warnings and disclosures in obscure EULA fine print hardly any non-lawyers can decipher.