Amazon estimated that each 1 ms of additional latency costs them a few million dollars a year as well as decreases rate of returning users. For low latency there is still nothing better than eventual consistency, so they may be driven by the bottom line. Also, from my experience of being a merchant on Amazon with hundreds of thousands of items in inventory that need to be updated almost realtime as prices/stock changes all the time, leading to a few millions updates a day (in bulk), I can't envision how Amazon would be able to achieve fast import from a horde of merchants like me on any SQL system.