With digital you're hoping the 'store' keeps it in storage for you in perpetuity so you can redownload/stream it. If you buy a DVD and lose it you can't go back for another free copy. There's definitely an issue that the original license should allow you to always download and backup your copy DRM free so you will always have access but most people aren't going to do that. I bought lots of music/video content from iTunes over the years and rarely back it up. The fact I can just stream it/redownload it from them is very useful but it's also unreasonable for me to expect that Apple should be hosting my 99¢ purchase for the rest of time.
it's also unreasonable for me to expect that Apple should be hosting my 99¢ purchase for the rest of time
That's fair so long as it was made clear at the time of purchase that you aren't buying the song, and that you're only renting it for a while. If they didn't put a clear explanation that you might lose access on the page when you clicked buy, and not buried deep in a 50 page EULA, then it is entirely reasonable to assume that Apple can afford to keep a 5MB file available for streaming forever, or until Apple closes down its streaming services.
> With digital you're hoping the 'store' keeps it in storage for you in perpetuity so you can redownload/stream it.
Not necessarily. What if the store didn't have to do that?
That's not a great example, because once I pay Apple I can copy the song to my local device and keep it myself. I would hope Apple would keep it on their servers ready for me for the rest of my life, but if I don't I can still access my purchases.