It's ironic that Steamworks being open and honest and easily controllable actually makes people like it less than traditional rootkit-style, background-running sneaky bastard DRM methods.
One of the things I do is IT network security related stuff. I've done a whole lot. In my travels I have for example seen rootkits (the real thing), worked with installs which were compromised but not rooted, been the one to put in code which intercepts TTYs to see the text being typed (its like a keylogger only deeper), did a thing which, in terms of function, worked the same as a "man in the middle" attack, and other stuff including kernel and other source edits. This is all white hat stuff, done in networks I'm supposed to be in. I've been a lot of places with this topic and I don't mean theoretically. It's one of the things I do every day, including today.
I say all of this to make a point and make it have some weight.
A rootkit is as a rootkit does.
A little program which screws around with some kernel edits (for example) and is a nuisance is not in my opinion a rootkit. Any SecuROM which may have come with Fallout 3 did not rootkit my windows workstation. It may (or may not) have done something rude (I never noticed anything), but it did not resemble a rootkit.
However. In order for me to feel comfortable installing Fallout NV, I am in the process of making a separate OS install on a separate hard drive, and taking a number of other precautions I'd sooner not go into here. This is because steam will endeavor to cause my workstation to connect into their network and exchange data. That is a different world from a program which stays localized.
I am not going to these lengths because I think it is fun, or because I'm misunderstanding something. It's because a backdoor is as a backdoor does. This has the arrangement of such. Once a data leak has happened you cannot reverse it (unlike a rootkit which you can cleanse out of the system). So, you have to be proactive on something like this. You can't watch it happen and then say "oops look what it did."
If I had a 100% dedicated gaming PC, with dedicated hardware, and no information on that machine which I felt was a compromise to either myself personally or anything I do, it would perhaps be acceptable to use fewer precautions. But well, such is life (donations for my dedicated gaming rig can be paypalled to ... umm, nevermind).