RT desktop isn't just for Office!
Even Tom Warren is liable to post stuff like this:
Windows RT still features [...] a crippled desktop mode kept around for the sole purpose of offering owners a semi-touch optimized version of Office.
Windowed multitasking is still essential for a lot of tasks. Consider writing a research paper, or studying for an exam, where you need to examine a variety of documents / webpages all at once, in conjunction with your notes. iOS or Android-style multitasking is terrible for this. Metro "snap" mode is not much of an improvement.
(Aside: note the act of "writing" is not monolithic. For all-at-once emailing or off-the-cuff blogging, basic/no multitasking is OK. Research-style writing is better suited to WIMP-style multitasking. This is the sort of thing Microsoft users refer to as "real work.")
RT desktop isn't going anywhere, nor should it. Instead, I think desktop-style apps will be added to the Windows store.