I don't really like this idea, maybe if I was a care free windows user who didn't care about my bank account, but the thing is it's just not safe having 1 account for all, if your account gets taken over, your SCREWED!
It wouldn't mean your passwords was insecure either, there are very powerful bruteforce crackers out there.
Take my advice, USE INDIVIDUAL PASSWORDS ON EACH WEBSITE YOU REGISTER ON.
From the page: "As many know Amazon has a new music downloads service, the downloads are all DRM free (Woohoo!) you can download individual songs without the downloader, but that would take more time and cost more money."