Are you sure they ever were? There used to be (and maybe still are?) movies for sale in the store that were not available for re-download from the cloud (e.g. until about a year ago that was the case for all Fox movies). In those cases there was a disclaimer on the movie's store page ("this movie is not available for downloading from the cloud" or something similar).I have two movies that are no longer available in the cloud.
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Well, to me more precise, due to the escape clause in the Terms and Conditions quoted above, Apple does not have a legal obligation to offer the movie for repeated downloads forever.It's not like that at all. This is what people misunderstand about buying from iTunes. You only "own" the copy you download, you don't own the copy iTunes hosts to allow you to download your own copy.
But of course they also know that it would damage their business if that were common-place, so I'm pretty sure they will avoid that at all cost. It would be particularly bad for customers who only stream movies (e.g. through the Apple TV) rather than downloading them. The same of course goes for other services like Vudu.