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.
When the stars threw down their spears
And watered heaven with their tears:
Did he smile his work to see?
Did he who made the lamb make thee?