In a few comments to my last post Danny says that RSS feeds from Apple and Microsoft music stores are not standard:

comparing the Apple and MSN data it only goes as far as being XML with a root <rss> element.

It's true, both feeds don't validate.

When I first found those feeds I didn't check their code, I subscribed them with my aggregator, and they worked. This is what most users will probably do.

I'm not saying that standards are not important, they are, Apple and Microsoft should do their best to fix their feeds. But I appreciate the fact that while in a perfect world there might only be one standard and no errors, in this word we have a bunch of standards and a lot of errors. Still we manage to improve a little every day, allowing users achieve new things with new tools. Isn't this cool?