Only those running admin accounts benefit from this feature. If you run Chrome in a limited user account on Windows 7, or a Standard User account on OS X 10.7, Chrome may or may not prompt you for an admin password (depending on the configuration). I've always had to quit all my applications, log out of my everyday account, login as admin, update, logout, then login again.
From my experience Chrome installs itself into %appdata% to avoid requiring admin permissions. And not once has Chrome asked for my admin password on OS X.
Right, that's one way of installing Chrome on Windows. However if you install Chrome for all users, then you pretty much have to start Chrome with an admin user's UID. I get prompted for my admin password on OS X, as I work in a standard user account.
I maintain two accounts on OS X: one for software installation & updates, and the other being my primary account with limited credentials. That way, if I were to accidentally run some malicious code, it wouldn't hose the entire system.
So Google Chrome.app resides in /Applications, but it's installed by the account that gets created when you reinstall OS X (which is by default an account with full privileges). Standard users can read /Applications, so they can launch Google Chrome.app, but the process can't write to /Applications because of its effective UUID. That's why it prompts for an admin password.
