I disagree. There's plenty of other uses and potential (heck, they can hold up to 50GB) in these warring next generation optical formats (Blu-ray and their mortal enemy, HD-DVD), and that's exactly the point: these formats are in the middle of an industry polarizing war, and I think Apple hasn't committed to including either in their machines because they don't want risk leaving their customers high and dry once the dust settles and (dear lord, finally) one format wins out. The iTS/movie downloads/iTV theory doesn't hold water in my book also because that would mean they should eliminate CD and DVD drives from their machines - after all, those drives can undercut their iTunes Store music and movie purchases, right? These discs can hold a lot more than simple movies.
This ridiculous Blu-ray/HD-DVD situation is Betamax vs. VHS all over again, and while Apple is known for pushing the envelope on which technologies they adopt, I believe they're simply waiting for an actual standard to emerge. The only question is when these camps are going to get over themselves and stop forcing consumers to stock up on Advil for every trip to the electronics store.