It's true, in short, that Microsoft is probably feeling the pinch of Linux's growing acceptance; if you can't beat 'em, as the old saying goes, you might as well join 'em. After all, Microsoft was recently a LinuxCon sponsor, among other contributions.
(Phoronix's Larabel was also the one who first picked up on Valve's plans, as far as I remember.)
Cost vs. benefit
On the other hand, Microsoft Office has always been a big cash cow for the company, and the new Office 2013 and Office 365 are still hot off the proverbial presses.
It's already the case that some users are questioning whether these new entries are worth the money, particularly in light of all the free and open alternatives out there and widely embraced by Linux users.
Microsoft also doesn't exactly have a history of embracing Linux. A "cancer," in fact, is what Steve Ballmer once called the free and open source operating system. Even OpenOffice has felt Redmond's anti-open-source wrath.
What about Chrome OS?
That's far from clear. At best, the most I can envision is that Microsoft might offer a version of its browser-based Office 365 for Linux users.
An even better idea, though, could be to port Office to Chrome OS and thereby "ride on the Chromebook's coattails," as Linux Advocates blogger Dietrich Schmitz recently suggested. That, in turn, "would give them entrée to the Chromebook market of extensions," Schmitz pointed out.