In other words, Steam doesn't even ask for any personally identifiable information.
You may wish to review
Valve's Privacy Policy where it states it does collect -- in their own words -- "personally identifiable information".
From that link:
""Personally identifiable information" consists of a user's name, email address, physical address,
or other data about the user that enables the recipient to personally identify the user...". (emphasis mine).
Note the incomplete and open-ended definition, and that Elizabeth 2k was unable to provide a link/etc. for this, even though she said that information was public.
Regarding privacy of personally identifiable information:
"...Valve may allow third parties performing services under contract with Valve to access stored information but such access shall only be to the extent necessary to provide those services. In those instances, the third party will be bound by the terms of this privacy policy..."
However this isn't always the case:
"Personally identifiable information protected under this privacy policy and collected from users may be done in conjunction with associates under agreement with Valve... Valve's privacy policy does not extend to associates of Valve."
So Valve does collect personally identifiable information, they don't specify exactly what personally identifiable information they collect other than the obvious unobjectionable bits, they share said personally identifiable information with both third parties and associates, and the latter aren't bound by Valve's privacy policy.
Some idea of the unspecified personally identifiable information collected and shared is possible by perusing Valve's
Steamworks API Overview page.
The API overview page also gives an idea as to what things steam/steamworks is doing while running in the background.
Remember that while you don't need to be online to play a single-player offline Civ5 game, you do need to have steam/steamworks running in the background while playing a single-player offline Civ5 game.
One thing that's running is VAC (valve's anti-cheat):
"VAC is a component of Steamworks and the Steam client, and works by scanning the users system for cheats while your game is running. It works a lot like a virus scanner, and has a database of known cheats to detect."
So for those of you who are cheating yourself while playing a single-player offline Civ5 game -- you're busted!
That'll teach you to play with your cheating self...
Seriously, how is having an unnecessary virus scanner-like anti-cheat service constantly running in the background, for a single-player offline game when cheating is not an issue, a 'benefit'?
That's merely 1 example of why having the unnecessary steam/steamworks running in the background is not desired by some of us, and why steam should be a choice and not forced upon us.
Folks who want steam should have that choice. Those of us who don't want steam want that choice as well.
Steam is presented as a benefit to players, but it's more than that. Yes, it benefits some players, but it's a double-edged sword and that part is being glossed over in the attempt to sell us on steam's benefits to us.
Reality is that what's most important is that forced steam benefits steam and 2k and firaxis. Take-Two's (Take-Two Interactive Software, Inc NASDAQ: TTWO) first and foremost obligation is to their stockholders, not customers.