Revenue growth comes from both new customers and existing customers. As Assure includes many large companies like Walmart and where AWS has more startups that’s likely important. Let’s suppose Assure increases revenue from existing customers by 4% (inflation + growth) 18 * .04 = .7B and AWS increases by 8% (inflation + growth) = 36.1 * .08 = 2.9B. Which would mean 10.6 - .7 = $9.9B revenue from new customers for Assure and 12.6 - 2.9B = 9.7B revenue growth for AWS from new customers. The difference in customer bases may also be important in a downturn as Walmart is far less likely to fail than Imgur.

Granted, I chose those numbers to arbitrarily get that result. But, it also demonstrates the other reason to use percentage growth, inflation on a large customer bases implies growth where none exists.

PS: I realize they both have large and small customers, my point was not about AWS vs Assure but % vs $.