Yeah, the term RTM no longer means "final" like it used to. It's more like shipping a late release candidate, then hoping by GA Windows Update will install the actual finished parts.
It's understandable that they didn't want a bunch of review articles popping up insinuating that it's the final revision of 8.1 when customers with Internet connections would essentially be getting revved to a later build during installation.
They should not have called it RTM if it wasn't really RTM.
I've worked at a few software companies and none of them have used these terms quite the same way.
They can still move to a rapid release cycle and have a solid RTM. Chrome and Firefox manage to do it every 6 weeks.