[sanderjd]

That is something they do, which I strongly dislike, but it isn't their business model. Their business model is "pay us to run things on our infrastructure instead of building your own, with an option to be billed based on your usage".

The "take a popular OSS system and provide it as a service" thing is a complement to that business model, because they can say "now that you're using our infrastructure, you can also use all these services, and we'll manage it for you, and you'll only have a single vendor to pay". It provides additional value and lock-in to the business model, but isn't the essential part of it.

And no, that isn't where it began. Providing managed services for open source systems was not a part of their initial value proposition. When I started using EC2 (with EBS and S3), one of the tricky things was getting our own database infrastructure to work reliably on EC2.

It's true that RDS was released not long after, and did the "take a popular OSS system" thing, but they really didn't embrace that model until years later. Indeed, I think RDS still seems like second fiddle to their proprietary non-relational DB service.