You're right, but there's another concern: who maintains the software? The original developers forming a company that supports development is not possible if the company is not protected by the license in some way.
Under the AGPL, the source-disclosure provision persists.
In both cases, Amazon is doing software development, but in the first, they're not contributing back to the codebase. In the second, they are.
Amazon are maintaining the software. Along with other users.
Note that AGPL applies to few projects at this point. Amazon is very heavily reliant on, e.g., Linux and Xen, both of which are GPL v2.