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.
