The screenshot you're referencing is from OS X! If you don't quit Chrome for a while, then open "About Google Chrome", that dialog or something very similar will display.

Oops, my bad! I do quit Chrome accidentally from time to time (Cmd-Q being neighbor to Cmd-W).. Thats probably when Chrome is updating.

Likely because you restart the machine (due to e.g. Safari updates or whatever) often enough for this not to happen.

That hasn't been my experience. I run Chrome on 10.6 and when a new version comes out, I have to manually close/reopen Chrome to install it (usually by clicking the "Update and Restart" button shown in that screenshot).

It seems to me that the update process is slightly more jarring on OS X than it is on Windows (though I haven't used the Windows version so I am just assuming). When I finish using Chrome on OS X I will close the last tab with Cmd + W, so Chrome is still open and therefore it won't be able to install the update next time I open a tab. On Windows I would close the last tab and the application exits completely – though it might take slightly longer to open Chrome each time, I will never really have to manually restart Chrome to get the update installed.

Just depends on your habits, I always Cmd+Q my applications when I'm done using them.