You do know that after installing the downloaded deb it adds the google apt repository to your sources and adds the key so that all future updates are done the apt way? (You can also edit files to prevent this behaviour.)
Now after this change it becomes analogous to "the App-Store-only way unless you are technically inclined enough to google up how to workaround". Definitely not "the same model that every Linux distro uses".
The closest thing is Android, but Android has an obvious easily accessible checkbox "Allow installation of non-Market apps". Chrome didn't get such a checkbox in Options (nor a toggle in chrome://flags/).
Technically, there is a new command-line switch, but its current full name was never mentioned even in the related bug tracker issues (http://crbug.com/128748, http://crbug.com/55584). You have to look into the source code to find it: --enable-easy-off-store-extension-install