I doubt Microsoft will offer a $15 or $30 version of Office for iOS, BlackBerry, or Android. Yes, Office Mobile 2010 will come with Windows Phone 7, but I doubt that platform will take off, so it won't matter.
If you think I'm nuts, consider what's already happened to Adobe Systems and its Acrobat product. Once Apple added PDF annotation to Mac OS X Snow Leopard's built-in Preview app, the need for both the free Adobe Reader and the $449 Acrobat Pro dropped significantly among Mac users. Acrobat Pro has picked up more and more capabilities, but they are relevant for a tiny fraction of the user base. Mac users have largely abandoned the pricey, full-featured Acrobat unless they are creating Acrobat forms or doing PDF-based publications that need its security management and hyperlinking capabilities. On Windows, Adobe offers the less-capable $299 Acrobat Standard, but not on the Mac -- that product's "middle market" evaporated when Preview incorporated the Acrobat capabilities that most users needed.
I can see the same shift occurring for Office over the next few years as mobile users realize what they've always whispered: "I really don't need all that stuff in Office. My mobile app does just what I need." Hmm, maybe they'll wonder to do with all those Windows Server boxes (excluding Exchange, of course) that they realize they don't need, either.
This article, "How mobile will kill off Microsoft Office," was originally published at InfoWorld.com. Read more of Gruman et al.'s Mobile Edge blog and follow the latest developments in mobile technology at InfoWorld.com.