I get the feeling that
(a) Amazon cares little about Linux, and
(b) the Amazon MP3 downloader was done by very inexperienced or very poor developers.
Linux is a very small sliver of the market, so (a) is unsurprising.
My reason for casting stones at their developer is that the downloader does not work with 64b CPUs and now when I try to install it on a 32b Ubuntu 10.10 I get the message Dependency is not satisfiable: libboost-filesystem1.34.1. After installing version 1.42.0 of the libboost filesystem, I still get the error message. This strongly suggests that someone coded the dependency checks for only one version of the library, or wrote the code not considering the possibility that newer versions would be backward compatible.
I like Amazon, though I am done dealing with Amazon Sellers. Tonight Amazon had me thinking I might have to go elsewhere for MP3 downloads. However, a little googling and then a moment in the Ubuntu Software Center led to clamz. It appears there are a few other tools to do this, but clamz is the only one I see as an officially-supported Ubuntu package. And it works (or at least on the one album I pointed it at tonight).
I prefer using clamz over the Amazon downloader, because it's less closed software on my machine. Clamz likely does it's job, and nothing more. The Amazon downloader, for those lucky enough to have a system it works on, has always been an unknown factor--it downloads MP3s, but does it do something else? Probably not, but one never knows.
As an aside, the MP3s that I downloaded tonight do not have the same identifying information as the ones I wrote about last week. It may be obfuscated, encrypted, or just not present.