On the technology side Apple has actually built everything necessary (AppleTV + iTunes streaming) but the problem is dealing with the content silos.
If Apple could it would simply license all the content and stream it to customers either for a standard price (e.g. $1.99 per episode of 480p programming, $2.99 per episode of 1080p) or via subscription (e.g. MLB/Netflix) or ad-supported (e.g. Hulu Plus).
The only reason AppleTV isn't TV nirvana (at least in the US) is licensing issues. (BTW you can program an AppleTV to recognize any remote, so you can seamlessly make you TV remote also control your AppleTV, without even switching modes).
In case you're wondering, the basic problem right now is that TV networks get paid about $2 (I did a bunch of back of envelope calculations, so I may be significantly off, but it's in this ballpark) in advertising per viewer-hour, so if a family of four watches an hour of TV, then the network gets about $8 in ad revenue. Apple is offering $1.40/h, and it's also messing with DVD sales and syndication so there's a big gap there.
Now, I seriously doubt that the production company that makes the content gets much of that $8, so if Apple could deal with content producers directly...