I'm pretty sure companies would not be happy if they found out Amazon was tracking those companies' customers. If it got out, it would probably be huge. Not worth it for Amazon to do this.
The only practical way to do such tracking reliably would be to inject html into every page loaded from one of their CDN's. That would be visible to everyone, and they don't do this.
Hence, either they have fairly ineffective IP address based tracking, or no tracking at all.
They wont need to add cookies or anything like that. They can track you just by parsing the connection logs on their routers and switches. Also every thing that is billable is logged. So technically they are already tracking and recording every access across their network. It is impossible to verify if they actually do this without anyone leaking information that worked on the system.