Anything involving Amazon is definitely going to move a market as they are the most profitable online retailer in the world, so it is possible there could be more upside once they make some sort of official announcement on the subject. They would probably prefer to keep it low key so it feels like a bit of a slip-up for them to disclose the information in such a way. I have a feeling that they will build up an enclosed ecosystem like we've seen at Paypal, where people can pre-purchase and store Bitcoin internally within their systems. After that they can profit from internal transactions that are essentially free compared to paying a small cut to payment networks like Visa or Mastercard.
We should still not forget that Bitcoin has transaction capacity issues. If Amazon were to accept only Bitcoin and no other payment method at all, we would be screwed. Their revenue is so high and their transaction volume insane, we would quickly be running into a deadlock as Bitcoin couldn't scale quickly enough. It is good news on the one hand, but it would be even better if we knew that Bitcoin could live up to the challenge technically.