[TeMPOraL]

> My interpretation is that Google is "un-training" users from using this valuable piece of screen real estate for a useless no-op function, (...)

It's not an useless no-op function. By going to default/main page of the service it reverts you to a known state, simplifying navigation and enhancing user confidence. I personally rely on this behaviour of main logos and get terribly annoyed if someone breaks my expectation (which, rarely, happens).