I'm going to have to go with Guden here as well. This isn't even a matter of "fault". It is silly to assume a company will open their standard to help a competing companies product out (although not competing in this space). Nobody should have assumed it would work in the first place. A choice by Apple, which is really the only logical choice they could have made, does not mean they are somehow guilty of denying users something they were gauranteed to begin with. When I got an iPod I expected to be able to play music on my iPod, and not on a console that isn't even out yet, which has no relation to the company that the iPod was made at.
Fault implies that they did something wrong. What gave anyone the idea that the right answer was to allow MS to play Apple's DRM (which is what saying Apple is at "fault" means)? Its like iTunes playing Sony's Connect DRM music or Connect playing iTunes DRM music -- as nice as it would be to have one common ground, thats not the world we live in and we can't just expect companies to throw away their goals as a company to help out another company (with often conflicting sets of goals). Neither company did anything wrong here. It is the way business works -- both made choices in their best interest (the arguement that it being able to play music on an Xbox360 is somehow in the best interest of consumers is moot -- the best interest of a few customers who would actually do it, but is that worth all the costs involved?); MS did what they could to provide a feature that might interest someone at very little cost to them, and Apple made a choice not to support MS in their endeavour to make the Xbox2 have more bullet points on their box (no surprise -- it is infact their DRM -- if you really wanted to you could get around it by burning them to cd and then ripping from the cd to mp3, worst case). Additionally, whos to say that MS's offer to Apple was very compelling to begin with -- how can we be sure that it was Apple who turned down the offer of their dreams? Chances are Apple didn't see any real benefit to them, because the feature will likely go unused by 99% of the people out there and opening up a standard/licensing it out opens up a huge can of worms. Who is this feature benefiting that didn't already have the ability to do something similar and just as easily? And what percentage of those people would the ability to play DRM music affect (I know several people with iPods and no DRM music)?
The only one at fault here is a user expecting to actually do something as silly as play DRM music on another device outside of what it was made to play on.
This really isn't such a big deal, but at the heart of this is a major problem with a lot of industries and consumers -- people expecting things they shouldn't logically be expecting. Dare I say, most angry/unsatisfied customers have their roots in this situation.