In 2005 (IIRC) Microsoft released a media initiative called Plays For Sure along with a number of both device manufacturers and online music stores. The idea was that you would be able to buy any number of devices from different companies, then buy music from different stores and be sure the music would work with the player. Well, it seems Microsoft has had enough of this idealistic "partnership" or "play nice for the consumers" thing and is going back to their old practice of locking everyone out: their new Zune players are incompatible with music bought for the old stores and the old players will not be compatible with music from the new Zune store. Yeah, that's why people still buy Microsoft products / services, they like having to re-buy everything every two years. Good on you, MSFT!
Now, lets compare that to Apple's iPod and iTunes Store: every single iPod sold since the beginning is still able to play music from the store today, and every new iPod is still able to play music bought from the store on day 1. Yes, it is vendor lock-in, but at least they tend not to give their customers the shaft quite as often. And they have BSG ;-)