While I would not consider Steam to be a poor drm design (I actually like it), there is one really frustrating feature of it. I have multiple computers, and multiple games. But if my 4yr old son wants to play our Train Simulation game on one computer, and I want to play a different game on the other computer, can't be done. That's my only gripe about Steam. Other than that, I can't see how people can find it difficult.
In no western country is it legal for two people to play the same game using the same license. That is not a Stream issue, as Digit pointed out.
Exceptions to every rule...
Yes, you can make a backup, but can you restore that backup if Steam won't work? (doubtful).