Note there is an implied drm baked into nearly every steam game, They will only run if they find a authorized steam service running.

Now my understanding is that this is fairly easily bypassed, I think you need a fake steam runtime, but it is still drm.

And as a final thought, despite this, steam is still heads and shoulders in front of any other online service I have used in respecting it's users. I like how you can share games, you have to jump through a few hoops, but it is is easy enough to do. As great as this is, it still is very heavy handed in "managing your digital rights" (said in as sarcastic a tone as you can manage)