Pretty sure the answer to that is no, they haven't turned to rocks. I believe Amazon keeps a record of your book purchases, and Amazon isn't going away tomorrow, so you should be able to redownload your books (and probably even back them up). If so, all is good there (relatively speaking).

Sony also keeps records, but good luck redownloading your PSP game. Or your PS3 game for that matter. But at least in that case, if you already have it downloaded, you can still play your game. Sony couldn't come down from above and turn your game into a rock.

The Crew for PS4 on the other hand. You can (probably?) still redownload that, but that doesn't actually do you any good. Ubisoft did come down from above and turn that into a rock (there is no good reason to make a single-player gamemode online-only).

Amazon may not be going away tomorrow, but they have form for disallowing redownloads of old ebook purchases. If you dared to buy ebooks from them pre-Kindle, you can't access them anymore. If you hold onto your Kindle devices for too long instead of replacing them with a newer model, you can't access your old books that aren't already downloaded until you buy a new device.

For now, Sony has no issues with people redownloading PS3 games. Or PSP games onto a Vita - not sure if you can still download onto an original PSP. They'll probably jump on the Amazon revoke-download train eventually, though.