Open ... and Shut Windows is dead, and Microsoft Office has killed it. Or will, once the rumours about Microsoft porting its wildly popular Office product to the iPad become reality.

For just as porting Office to Mac OS X back in 2001 sowed the seeds of Apple's relevance as a credible desktop alternative to Windows, so too will Microsoft's capitulation to the iPad ensure that Windows will die even as Office takes on a new, multi-billion dollar relevance.

Microsoft, however much it may want to own the customer experience – from database to operating system to applications to free-time leisure gaming – wants to make money even more. Right now, Microsoft's only real money in mobile comes from browbeating Android licensees to pay it patent hush money. So Microsoft needs a winner in mobile, and Windows isn't it. At least, not anytime soon.

Which brings us to Office. Back in 2000, I was tempted by the Mac, but couldn't justify buying a machine that locked me out of the indispensable tool for business: Office. This changed in 2001 when Microsoft announced it would be porting Office to Mac OS X. Game on for the Mac.

Arguably the iPod and iPhone have had a bigger halo effect on Apple's Mac fortunes than Microsoft Office, but for many of us, buying a Mac would be impossible without Office, no matter how cool Apple's iProducts.

Putting Office on the iPad is a return to pragmatism-over-politics for Microsoft. After all, Microsoft zealously shored up its Windows franchise with Office for years.

The one platform Microsoft is not rumoured to be supporting anytime soon is Google's Android, just as Office-on-Linux remains a chimera. Microsoft, despite its newfound respect for open source, isn't about to seed the open-source market with its crown jewels. Office is a kingmaker in the enterprise, and the iPad is already king there. If Microsoft wants to make money from Office, it has no choice but to support the iPad.

But Android? Or other Linux variants? Not a chance.

Let's be clear what this means. Apple is already on a tear, but with Office on the iPad the floodgates will explode on enterprise adoption. I don't have to use Office much anymore - for me, it's a relic of an old way of computing - but I keep a copy for those times that it's a requirement. Once I have that on my iPad, the utility of carrying around a laptop, even my super-svelte MacBook Air, is gone. Forever.

And in that brave new tablet/smartphone world, Microsoft is currently a non-player, and unlikely to make up ground against a surging Apple. Sure, Office sales will go through the roof, but Windows sales? They'll evaporate, because they largely come from a form factor (desktop/laptop) that will hemorrhage market share.

ZDNet's Larry Dignan calls this a "smart way to defend the franchise," and that's true of Office. But it's a sure way to annihilate the Windows franchise.

Microsoft denies that it's porting Office to the iPad, but this is bunk, as The Daily insists. Microsoft has no choice but feed Apple's iPad success. It's not yet ready to also embrace Google's Android success, because while Apple is a hardware vendor, Google competes with Microsoft on a number of fronts.

And open source? It competes with Microsoft pretty much everywhere. No way is Microsoft going to aid and abet its own downfall by putting Office on Linux.

Still, it's a big bet Microsoft is making here, one that leaves it both a big winner (Office) and loser (Windows). Microsoft has to choose which of its cash cows it's going to kill. Actually, that's not quite true: Apple has decided that Windows is dead, and Microsoft has finally accepted this fact. ®

Matt Asay is senior vice president of business development at Nodeable, offering systems management for managing and analysing cloud-based data. He was formerly SVP of biz dev at HTML5 start-up Strobe and chief operating officer of Ubuntu commercial operation Canonical. With more than a decade spent in open source, Asay served as Alfresco's general manager for the Americas and vice president of business development, and he helped put Novell on its open source track. Asay is an emeritus board member of the Open Source Initiative (OSI). His column, Open...and Shut, appears three times a week on The Register.