Microsoft's rush to introduce a new OS every other year or so is a terrible strategy. While I understand the desire to bury the Windows 8 name, that is the only advantage and I'm not sure it is enough to counterbalance the disadvantages.
Microsoft seems to think they need to release a new OS to stay competitive. The thing is, people (with the exception of techies) do not BUY operating systems. They take what is on their computer, be it Windows98 or Windows8. Generally, people do not care about operating systems. Their care that their applications will run, and that their workflow will not be disrupted by a new GUI. Neither of these can be assured if Microsoft keeps pumping out new versions of their OS every few years.
Microsoft has a mistaken belief that they need to reinvent themselves every few years, that it is the chrome that sells their product. They are wrong. It is the 20+ years of backwards compatibility that maintains their dominance on the desktop. Their current strategy is directly threatening their core strength. It may not bring them yearly growth, but when you already have 90% control of the desktop, there really isn't that much to grow into anymore.
Of course, the market /is/ changing. Desktops are no longer the sole computing devices in use by the general public; tablets and smartphones are directly threatening that hegemony. Frequent changes to the core software of the desktop, however, is not going to revitalize the desktop market, however; it will only fragment and weaken it. If sales are declining, it is not because the OS is at fault but because people are buying fewer new computers overall. Microsoft should branch out into new markets with WinRT and WinPhone, sure, but do not do so by cannibalizing their main market.
Microsoft needs to focus on its core strength and not rush new versions to market in vain hopes of recapturing the glory days of the early 2000s. Incremental upgrades, not complete reinventions are the name of the game. Neither end-users nor businesses are clamoring for a Windows 9. Upgrade Windows8 to a usable state (e.g., kill Metro) and then keep it up to date with further upgrades throughout its lifetime. If they keep selling that for ten years they will do fine. Only release a new version of the OS when it is actually necessitated by the technology, not by marketing.
Microsoft, give us a Windows8SE, then live off the OEM sales for five or ten years. Take the time to create a new, stable and well-tested version of Windows instead of rushing into the next Vista or Metro. The users will appreciate having a platform that is not subject to upheaval every other year.