Musicmatch, first known for its jukebox player software packaged with many PCs and sound cards, was one of the first online digital download music stores for the Windows Media platform...I'm reasonably certain their online store beat Napster to the punch. The two services have been largely similar: both offer Windows Media protected format music downloads, at 99c per track or (usually) $9.99 per album. MSN music joined the fray recently with a similar service, but their store is so terrible and difficult to use that I have to assume they've "thrown the game" on purpose, to let the third party ecosystem of music stores (and broad support for WMA protected format) flourish.
Both Musicmatch and Napster also offer subscriptions that give you unlimited access to a majority of their libraries, with the ability to stream or download the files, but not to burn them or copy them to other PCs or portable devices. The subscriptions are a terrific way to explore new music. The Napster subscription is especially good, because they've built a Windows Media Center front-end to the service, so you have access to a huge library of music from your home entertainment center (i.e. your "stereo"). The software is buggy, but it's worth putting up with the bugs because there's so much good music, all available from your remote control.
Recently, Napster upped the ante by offering a $15/month subscription that works just like the aforementioned one (which is only about $10/month) but also allows you unlimited copies of the downloaded files to portable music players. Not bad. But the plot thickens. Yahoo bought Musicmatch a while back, and through that acquisition is now offering Yahoo! Music Unlimited, its own subscription service with unlimited copying to portable players. Better yet, it's only $4.99/month if you pay for a year's worth of service ($6.99 on a month-to-month basis).
This means Yahoo, arguably the most recognized brand on the Internet (OK, maybe 2nd or 3rd at this point), has standardized on Windows Media and "Plays for Sure" as its platform. There are now a lot of music services on Microsoft’s platform, and one of them is HUGE. How many sites use the AAC format in a form compatible with Apple's iPod? Just one that I know of: iTunes.
Furthermore, Philips and Microsoft have jointly announced the release of a new chip set for portable players that has Windows Media baked right in the silicon. Strike two for Apple.
Apple's iPod has a huge market share (something like 70%, I believe). Their hardware looks great, and people love their iPods. Most Windows Media-based portables look like cheap knock-offs by comparison. As a fashion item, iPods rule, and until Microsoft understands the fashion component of this market, their success will impeded.
But eventually Microsoft will get this part right, and even if they don't, it may eventually matter less and less. Sony's Betamax once had a fiercely loyal customer base and had the VCR market to itself. Then scrappy ol' JVC came out with an inferior format called VHS. They licensed it to every OEM under the (rising) sun and "VHS" eventually became synonymous with "VCR." The same ubiquity-to-also-ran-status transformation will happen to the iPod. And for the same reasons. Call me crazy. Just remember that you said that when the Windows Media Audio format is so universally adopted that no one will even notice anymore.