Steam

[Khendraja'aro]

I'm unaware of Valve using Steam to delete user saved games or purchases
or of any reassurances from Amazon that the titles will be unlocked if amazon or the ebook service were to go under.

This is possibly the most important part. This is what I was talking about with DRM that restricts what the user can do. Steam has no restrictions on how many times you can download, or on how many machines you can download to.

Uh, Ominous, that quote of yours is talking about "simultaneous access".

Do me the favour and try to access your Steam account from a second PC while you're logged in at the first one.

[Ominous Gamer]

Uh, Ominous, that quote of yours is talking about "simultaneous access".

Do me the favour and try to access your Steam account from a second PC while you're logged in at the first one.

With regards to DRM simultaneous means registered and/or authorized, similar to the number of simultaneous times you can use your Windows install key. Kindles after all can't be internet connected 24/7 to determine realtime simultaneous access
Here is a chat transcript that explains it

Him — You can download an unlimited number of times.
Me — If that’s the case why was I told that sometimes it’s five or six times and sometimes it’s one time?
Him — You can download an unlimited number of times to any specific device.
Me — So it’s not the number of downloads the way the rep yesterday said but the number of devices?
Him– Right.
Me– What if I get a new device?
Him — Most books give you six or seven devices that you can have it on at any one time.
Me — What about the 8th device? What if I get a new Kindle and new iPhone and they are eight and nine but are the only devices at the time that I am using.
Him — I believe we can release more licenses.
Me– You believe or you know? And does that mean that on my seventh Kindle I need to call Amazon and ask you to release each book one at a time?
Him — Well that’s up to the publisher
Me — Huh? I thought you said it could be downloaded an unlimited number of times to any device, could be on five or six devices at any one time and you could release more devices if need be. Is that the case or is it up to the publisher to determine? I’m getting more confused not less.
He said, “No, you can download a book an unlimited number of times.”
Me- Then why was I told there was a limit and for some books it is five or six but for others it might be just one.
Him- No you can download it and remove it and redownload it.
Me- That’s all well and good but yesterday I was told that there was a limit to the number of times it can be downloaded.
Him- Oh, well there is a limit to the number of devices you can download to but the majority of books let you download to five or six.
Me- So how do you know if it is one or six in advance? And what happens when I am on device number seven and the cap is six.
Him– To be honest with you that’s going to be a problem.

Once the item is on 6 devices, thats it. Doesn't matter which ones you're accessing at the time or not.

With Adobe Digital Editions, it doesn't even have to be unique devices, you could use up your 6 device limit by reauthorizing the same machine.