Some followup from John Carmack on that Quake3 sending information about your video chipset. Here is what he had to say originally posted on the /. forums:

This has been discussed before, and has been going on with the previous tests. The message of the day server was intended as a half-assed auto update feature that could be cross platform. We send a normal message most of the time, but if the version is out of date, we can send a message with telling you where to get the update.

I didn't want to deal with binary auto-updates on three platforms, and I worry a bit about security issues with that in any case. You can disable it by setting "cl_motd 0" when the game starts up if you really don't want to send anything or see our message.

We added the result of glGetString( GL_RENDER ) to get some much needed information about the distribution of video cards and drivers. We can see how many people aren't following directions and running glsetup. This is a big support issue. We can see how many people are running minidrivers, which are going to make our lives a mess in the future. We can see how many mac (steady 5%) and linux (5%at initial release, tailed off to 2%, probably due to dual booting) people are playing.

Getting this information has been usefull. We can compare the numbers of people playing with a given card with the amount of support emails we field, so we know which vendors (3DFX) we need to give more crap about their driver quality.
John Carmack

On top of that, here is what Tim Sweeney from Epic had to say at VoodooExtreme on the topic siding with Mr. Carmack that there is a bit of over reaction going on here:

"Unreal Tournament sends its version number to the master server / update server too. This is so the server knows what version of the game you'rerunning, so it can:

1. Update the .html news file displayed in the UT server browser. We use this to tell people with old versions that there are new versions available.
2. Give you a list of compatible servers.

The Slashdot guys are being silly. Don't they realize every internet client on earth sends information of this sort?

The IP protocol itself sends a protocol version number and (gasp) your IP address.
Internet Explorer and Netscape Navigator send their version number, as well as info about frames support, to all web servers, so the server can send you a page that's compatible with your browser.
The POP3 protocol sends your mailer's version number.
-Tim