You've been able to port MSOffice back and forth to PDA's since the mid 90's. It was built into Windows CE. This got them no traction for years. Why is it suddenly going to be a factor now?
Consumers won't switch to a new OS unless their apps are on it. Microsoft has had the big ones since day one including Angry Birds, Facebook, Twitter and the other heavily downloaded apps. What they will have a problem with are the less popular free apps like the ones offered from banks and the ones from stores like Starbucks that help you find them. There are also numerous free and useful apps like ones that help you find the cheapest gas in the area. If an app starts out small it usually is only written for iOS and then eventually Android. Windows 8 is way down the list.