When you download the setup for Google Chrome's site, you're only downloading the installer for Google Updater. The updater downloads Google Chrome's full setup and then installs the software. Here's an excerpt from a Squid report:
But sometimes you can't install the auto-updating software or you need to perform an offline install of the software. To solve these issues, Google Chrome started to offer a standalone installer.
Google notes that "the version of Google Chrome available from the link below may not auto-update to future browser releases, meaning you could miss important security fixes and feature improvements. If you install Google Chrome using the link below, bookmark this page and check back periodically to manually download newer releases." When I installed Chrome using the offline setup, Google added the auto-updating service.