Of course waiting to do a price cut till their competitor does leaves a bad taste in some customers' mouths. But I bet they think they're far enough ahead that it doesn't matter. Would Netflix and similar big AWS customers really leave AWS over something like this?
* This strategy even has a name: "follow the follower". Very common strategy in sailing.
At all times, companies in competitive situations have a basic economic model they use for pricing. Individual sales reps are allowed to cut price to X level for orders above Y quantity, and if they want to violate that price floor they need executive approval.
Simultaneously, the companies have models that are dependent on competitive pricing -- that take into account some assumptions about price and how it affects market share. When a competitor moves in one direction, the executives consult this model to decide how to respond, but at least in the situation I was in, the final decision of how much to cut price was a seat-of-the-pants decision by the EVP of Sales.
By "model" I mean an Excel spreadsheet, but I'm sure Amazon is far more sophisticated.
I'm not saying that either interpretation is wrong, but I think your use of Occam's Razor here says more about your assumptions than the nature of things.
I'm really just responding to the idea that "a mole" is farfetched. There's a reason that Apple is known for being incredibly paranoid about people leaking business secrets: it happens, often.
Interesting that they dropped by the same amount; either it was a lucky guess, Amazon adjusted their adjustment at the last minute, or AWS has a mole.