When I downloaded that Anouar Brahem album using Amazon's custom album downloader, somehow the tracks were stored at 160kb MP3 instead of 256kb MP3, the advertised compression rate. This puzzled me for a while, but I suspect that it may be a bad interaction with my iTunes CD import settings, which are 160kb AAC. Somehow, the Amazon downloader seems to have grabbed that rate and used it for my downloads, even though MP3 rates and AAC rates have nothing to do with each other. I've reported the problem to Amazon, I'll blog when I hear from them.
This is not surprising, it's a beta after all.