From the video, it becomes clear as day that Office 2013 is a "we-have-to-do-something"-release. The touch mode and many of the interface changes are cosmetic, and do nothing to address the core issue of Office simply being horrible for touch operation. Nothing has been done to truly design a touch-first, Metro experience for Windows 8, and considering Office is Microsoft's other big cash cow, it's unbelievable the company didn't put more effort into this.
The Windows and Office departments within Microsoft are separate from one another, and I get the feeling - although it's hard to impossible to substantiate - that the Windows team went ahead with Windows 8 and Metro before the Office team was fully on board. In fact, the Office team may even have simply waited it out, expecting Metro to be killed or shelved as too risky at some point. Now that Windows 8 is on the cusp of release, we are being a served a lukewarm Office update that feels and looks like a wart.
In fact, as I stated on Twitter, I'm actually convinced that the only reason Windows RT has desktop mode in the first place is because of the Office team lagging behind the Windows division. Had there been a Metro version of Office, the desktop mode would not have been part of Windows RT. You cannot install applications in the desktop mode of Windows RT, so it's there almost exclusively to enable Office to work. Save for a few specific settings which aren't Metro-ified yet (and perhaps file management), desktop mode on Windows RT could better be renamed to Office Mode.
As far as file management goes - it's a valuable asset, and there's actually no reason to drop back to desktop mode for something like this. Android has several fantastic touch file managers, and heck, even Windows 8 itself has an excellent base to build a Metro file manager upon: the file picker.
In the comments on the article at The Verge, people suggested that users increase the DPI, plug in a keyboard and mouse, and more of these things that have nothing to do with tablet computing and do not actually address the core issue. We've been offered a rudimentary glimpse on what an Office for Metro would look like with OneNote MX (this article is written in OneNote MX), but looking at Office's past release cycles, a Metro Office might still be 2-3 years away.
In those few years, Windows tablet users - ARM and x86 - will be dropped back to the desktop whenever they open an Office document, or whenever they need to change a setting which for some mysterious reason hasn't been Metro-ified yet or which doesn't belong on a tablet in the first place. Considering Windows 8 still has windows that do not even respond to a scrollwheel or touchpad scrolling (I kid you not - check the Character Map, for instance), that's pretty damn pathetic.