Windows RT will Include a Non Final Office Preview
As it says in the title, Windows RT will include today's current Office Preview, not the final version of Office 2013. Whether the RT owners will be able to upgrade free of charge is beyond me, but I'd assume that's probably what's going to happen. I just found this out on the Surface website myself, here's the article I wrote about it. http://techblitzblog.blogspot.com/2012/07/exclusive-windows-rt-tablets-will.html
Also, in a bit of shameless self promtion, here's the tweet that Paul Thurrott, well, tweeted.
Windows RT Tablets Will Feature Non Final Version of Office techblitzblog.blogspot.com/2012/07/exclus…— Paul Thurrott (@thurrott) July 21, 2012
Hopefully the Office 2013 preview is stable enough and feature packed enough to keep RT users satisfied until they get the update.