That information is extremely valuable to a competitor that is trying to catch up to AWS'. This information can also be passed along verbally and be 99% as a effective as having an up to date detailed revenue breakout spreadsheet.
So in this case he is taking some "secret sauce", which can be disclosed without ever being able to prove that it was.
Imposing an 18 month window where that person can't work at a direct competitor is sufficient enough to make that information somewhat stale and no longer as effective.
I'm personally against non-competes, but I did want to point out that there is cause for concern here. Also, as the VP of product marketing, he could have gone on to any job he wanted in any other cloud provider that wasn't a direct competitor, such as say Slack, Twilio, Box, Dropbox, I mean the list is pretty long. So it's not like his hands were tied in the job market. And certainly he signed the agreement originally, and should have modified it before hand if he was concerned. So it is possible that his boss at AWS is a bit irritated that he did not live up to the agreement that was signed. And as a VP you can't really claim that you "didn't know" about the non-compete since you will be doing a lot of hiring and imposing that very same clause on all of your hires.