I wonder if that is really such a big thing ...? Is Google (the Ad and online service company) really a competitor of Amazon (the online retailer)? In what way does Google make use of trends in online shopping? And furthermore: how many companies out there are harvesting emails, and what technology are they using? Most emails are sent using e2e encryption/Tls nowadays. Gruber mentions Edison Mail in the article ... are there more? And do webmail/freemail services sell these data to big data companies?
In that light, I think I like that move by Amazon. It protects their data and my data as well. Win-win.