It's impossible for any media to play on any platform. Even if something were supplied with no decryption key necessary, I can still point to some box it doesn't play on
It depends on why it doesn't play on that box.
If it could have easily played on that box, and would have worked except that someone went to extra trouble to make it not work, then people have cause to gripe. That's a situation where have people expending resources in order to achieve a lower total gross value, which is course, going to result in an even lower net value. If they simply hadn't spent the extra money to make it not work, they could have charged even more for the product. Purposeful economic destruction triggers a lot of peoples' bullshit alarms.
If it doesn't work, not because someone tried to make it not work, but because of a real limitation or practical concern, then that's a whole other situation. It's true that you can't play a movie on VHS player if you don't have physical access to the VHS tape, but why can't you? It's not because some evil or insane bastard wanted to make the media worth less. It works like that because it's easiest to make a media player which requires media, and harder to make a media player that is able to magically work without media. It's natural. It's like everything else in the world that we encounter (e.g. you can't take a trip in your car without physical access to the car) outside of the DRM sphere.
As long as someone isn't trying to keep it from working right, then I think most people will cut them a lot of slack. We're all quite familiar with, and more accepting of, mere technical limitations. It's when someone is dealing in bad faith and acting two-faced (anti-business in the market but claiming to be pro-business in other forums, such as their DC lobbying or their meetings with stockholders, etc) -- that we 1) get pissed off, and 2) give up and just do what happens to be both easiest and works best.
With rented media I'd expect DRM, it's the only way that system can work.
We have hard evidence that it works fine without DRM. From the late 1970s to the mid/late-1980s (I'm not sure exactly when Macrovision happened) we had a VHS rental industry without DRM. There was explosive growth in that period.
And the fact that Macrovision eventually showed up, isn't very good evidence that DRM was needed; we have no reason to believe the mid/late-1980s to late 1990s market would have gone much differently without it. And Macrovision was so trivially circumvented (a lot of people even did it unwittingly with literally zero effort) that it almost doesn't count as DRM (uhr.. "ARM?") so I could possibly even cite the entire history of VHS as proof that rentals don't require DRM to work. I suppose I could make a similar argument with the CSS on DVDs and the DVD rental market, but it's not quite the same (since people at least knew they were breaking the law when they played DVDs on "unauthorized" equipment, and from 1996-1999 AFAIK nobody had stuff like DeCSS yet, so the DVD rental market started with a situation much like the DRM situations that we have today).
With rented media, I don't understand the expectation that it should be downloaded locally and not copy protected.
Copy protection is easy to address: it's always a bad idea (no matter what kind of basic media tech we're talking about) because it limits implementations. When you tell mplayer users "no, our content doesn't work with your player, and we'll probably sue people if we ever find out that it does, so go look elsewhere" that simply can't be as good as "yes, we'll take your money." Anyone renting media should have an expectation that the business wants to do business and isn't going out of their way to look for reasons to say no and prevent the transaction.
As for the expectation of downloading (or otherwise making a copy of the rented media) you may be right or wrong, depending on the media tech. VHS and optical discs are great examples where I can really only think of one good reason where someone might want to copy the rented content to faster or more reliable media (if it's slightly scratched so it takes lots of retries but will eventually succeed) but that situation is avoidable by the business having their shit together.
With Internet streaming, I think it's pretty easy to see why it should be downloadable, because that's just dumb tech right now (in some markets, at least) so unlike scratched discs, the seller can't merely fix the problem by exercising more care.
One common case is that people's Internet connection is relatively slow, so it's hard (even in a best case scenario when the connection is dedicated to the stream) to transmit video in real time. My DSL is only 7Mbps, for example, so (very roughly) downloading 8GB of data takes around 3 hours. If we're talking about a 2 hour movie, then it simply isn't going to work; the bitrate is going to have to be reduced to even have a chance of working.
And maybe reducing the bitrate is a somewhat adequate solution, but an even better (and easier) solution is that I just go ahead and take 3 hours (or 5 hours or whatever is necessarily) to download the 2 hours of video. This approach is proven to work great but of course no streaming service offers that, since that's not "streaming." No legal Netflix clients have 10 GB buffers. (BTW, if Netflix didnt't have DRM, or if the DRM were easily and legally defeated, you damn well know someone would make a 10 GB-buffer Netflix client, which would give a business advantage to Netflix. This is what I meant above about copy protection limiting implementations. If the customer requires large buffers and the copy protection disallows the market from inventing that, then Netflix is essentially telling those customers "fuck you, don't pay me.")
Another common case for some people but not others, is that Internet connections aren't dedicated to streaming, or something [wave hands] out there is slow or bursty. I have a lot going on, on my network. I might actually have 7Mbps for watching a movie one moment, but it's going to be 2Mbps the next. Transmission and playback have just got to become decoupled. So there's your download example; in 2013 I'm really at least one order of magnitude of performance away from streaming being a good idea, and with DRM even the bad idea becomes unworkable.
Time will probably erase or mitigate the download requirement (but not the no-copy-protection requirement) . I know in some parts of the world, you have gigabit fiber to your home and even if your stream only gets 10% of your connection, it's good enough. Good for you. Maybe in 2023 or 2033 I'll have that my city. Until then, though, streaming is bad tech and saving the data for SATA playback is its only hope.
As for copy protection, time won't erase that uselessness. Both parties in the rental transaction have (and will always have) strong incentive for that to not exist. And if you don't have copy protection, then the whole download issue is kind of irrelevant anyway. Without the DRM, the industry will come up with players that do whatever is needed, and whether or not it solves the problem by downloading and saving, won't matter except to the consumers who are looking for the best tools for their jobs.