Just an example, I saw someone on DP with a PR5 astore, and claimed he got $2500/month with his niche (Play Station 3 Games) from organic searches. I'm not sure why he shared so much info if he really was getting as many sales as he did, but I did verify that his site was a PR5.
When you search on G! you can see that there are websites that only the frontpage is indexed e.x http://astore.amazon.com/your-id I believe that G! might ignore the inside pages. Is there anyone that managed to index an internal page e.x http://astore.amazon.com/your-id/103-abc&node=2
The reason he "shared" so much info was to get you to follow the thread back to his site where his "secret" involved buying text links and you can do it too by clicking *this link*, which brings you to Text-Link-Ads.com with his affiliate cookie on your machine. Does he really make $2500 a month on an astore? Dunno. Did he make some money off people who clicked through to TLA? Certainly.
I have a few astores now. My oldest is nearly 6 months old. None of them indexed by google at all I don't think. So it is possible?