Although the idea of having your data in the cloud is OK, it's just not practical right now. I have a 10Mb cable internet connection at home, great you think, stream no problem... But no, there are fair usage caps on this bandwidth which mean it's completely impractical. You pay for the speed of link here, but every ISP puts a usage cap on it. Once you start streaming all your viewing, it's no longer sufficient.
Same with my iPad. Yes I have a 3G contract, with 3Gb of allowance a month, but is that good enough if I listen to music and/or watch video all day? And this is over 3G, so not good enough to stream a HD movie without stuttering. Hell even BBC iPlayer struggles to be watchable at times over 3G, and that's no where near HD quality.
The other thing is the economy. Do you really want all of the content you've paid for residing on a companies server, with no backup of your own? Just think, Apple servers hold all your content, you've paid them for it. Steve retires and it all goes down the pan. Apple goes bust and you've lost ALL your movies and music. Now I'm not saying that is going to happen, but you just don't know.
There is a huge market for media servers, or else these home media content companies like crestron etc wouldn't exist, and there's an even bigger market IMO for a similar thing but lower cost. Apple are so close to doing it, I just can't see why they wouldn't. It allows you to use all your purchased content, purchase if you like as we do now to download, or stream your data from the cloud. Personally if they gave you both choices like this they must be onto an even bigger winner.
Pete