Is Windows 8 going to become rapidly irrelevant/outdated?

Although I understand fully the massive global reach that Windows has and the immense number of licences sold if they keep up the current three year upgrade cycle will the Metro touch environment not become rapidly outpaced by Android and iOS, both of which have much shorter development cycles? Each of those have witnessed huge development over the past three years, with Android undergoing a near complete redesign and Apple introducing many new features, including Siri and the Notification Centre. Although I feel that the traditional desktop/laptop paradigm may continue to be resilient in the face of long development cycles due to the vast upgradability afforded through applications, Microsoft and Apple have been unwilling to afford their desktop users new OS features outside of large, paid for releases. This could be lead to the Metro environment being rapidly outpaced by the quicker paced cycles of other mobile operating system, which Windows RT essentially is.

If Microsoft chose to accelerate the pace of the Windows RT upgrade cycle in order to combat the (near) yearly releases of Apple and seemingly random Android releases this would put the W8 Pro at a disadvantage in terms of features. However, if they updated the Metro environment for both Pro and RT this would potentially harm their ability to release new products with high prices, as they would be constantly updating the software pro bono and any entirely new version would have to be dramatically better to warrant the current WinOS prices. Unless of course they approached it as Apple have begun to with OSX, choosing to introduce incremental updates yearly for a nominal fee.

All in all I feel Microsoft may have come across a snag here (one that I'm sure they've already thought about and devised a plan for) as the desktop upgrade paradigm fails to combat the existing mobile/tabet upgrade structure and potentially has them two years behind their competitors in the mobile space by the time that Windows 9 arrives. I also don't feel that they can sell consumers software updates for tablets when Apple and Google both provide them for free, causing issues for Microsoft as it is still largely a software company, unlike Apple which can fall back on its hardware business and Google with its advertising empire.

What do you think they should/will do to combat this issue?