[the-rc]

I remember the spiffy demo where the thumbnail in search results morphed into the full Maps UI without reloading.

But unification had started even earlier than that. Pretty much since Larry became CEO again, he pushed this mantra of "One Google", which brought the infamous Kennedy redesign across all services, as well as more of them available under the google.com host (e.g. maps as discussed here, but also flights and more). One of the ideas behind the latter was that you had to log into your Google account just once, which gradually made it all the way to YouTube(!). I vaguely recall other factors, such as compensating for the increased latency from going HTTPS everywhere, but also discussions about securing and hardening cookies.

As far as I know, google.com/maps has been around the entire time, but perhaps now it might be simply the canonical URL in a larger number of cases.