NFC is just an example of a technology that won'r tun in AMZN's obsolete tablet. There are others, a consequence of it being made using a forked Android 2.1/2.2
USPS, UPS or facebook getting into e-commerce, is to highlight that AMZN does not have a moat, and indeed, is vulnerable to a host of different companies getting into e-commerce. AMZN sells because it sells cheaper, not because it has a moat. Selling cheaper without a cost advantage is not really sustainable. And AMZN does not have that cost advantage (that's why I mention operating costs/revenues, which are comparable to WMTs).
Also, once AMZN starts collecting sales tax everywhere, it loses that important, artificial, cost advantage.