How does WordPress track users

How does WordPress track their WordPress.org application users?

I mean, I believe that they keep a record of how many people are downloading it and how many are installing it and where. How do they do it?

Is it by pinging their server while WordPress is installed? Or something different? Anyone have any idea?

Update:
While Toscho answered the question, I just want to add some details. I asked the same question to Quora and Mark Jaquith (Lead Developer, WordPress core) answered it. Here is what he said –

WordPress installs ping the WordPress.org site to check for software
updates. We count the number of unique installs who have recently
pinged the site to get the number of installs.

WordPress.com doesn't ping us for updates, but they report stats
publicly:

http://wordpress.com/stats/

We take the WordPress.com number, and add it to the number from the
WordPress.org update pings, which gives us an approximate total number
of public WordPress sites. That's the number you're probably hearing
(it's currently over 36 million).