Nice. Microsoft heard complaints that developers had no early access to 8.1, so they reversed their stance and released it to MSDN subscribers.
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.
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.