"To solve latency, Amazon built Availability Zones on groups of tightly coupled data centres. Each data centre in a Zone is less than 25 microseconds away from its sibling and packs 102Tbps of networking."
25 microseconds at the speed of light (best case, through a vacuum; through fiber is significantly slower) is ~4.7 miles, and based on the quote, that is the furthest they are apart. If your buildings are within 1-2 miles of each other, they're essentially the same facility.
Sure, it's not geographically redundant, but nobody in this thread claimed it was. DinkyG disputed that your "one datacenter" claim was false, which it appears to be.