They do. But I'm guessing you don't scale up 1M+ servers for your Uber canary traffic tests - these are some of the scales Amazon undergoes in these events. The scale is unlike almost any other web property around.
Do they really need 1 million servers? Many of my friends who work at other tech companies need such few servers in comparison even with significantly high traffic that just screams massive inefficiencies...which seems wrong.
But I've never worked at Amazon so I wouldn't know.
But we didn’t handle free-form text search like Amazon. I can imagine that would necessitate a huge scaling up of compute and data.