Before Microsoft’s earnings, we brought you comments from the company that seemed to indicate that Windows revenue was set to decline in its most recent fiscal quarter. Gartner estimated that PC sales slipped some 1.4%. Microsoft said that it thought the number would be larger.

When the facts came out, revenue from the Windows division had declined some 6% from the same quarter a year prior. That number is hard to parse. As we noted, there were material, and potentially immaterial influences on the decline:

[F]looding in certain Asian regions led to supply restrictions that caused product bottlenecks around the world as plants that produce hard drives went underwater, and offline. The complexity of the PC supply chain makes it vulnerable to such issues.

Also potentially impacting Windows revenue is Windows 8, a product that has little issue causing press cycles. It could be that certain consumers are holding off from purchasing new computers or upgrades to Windows 7 in the face of the coming Windows 8.

The question is which, if either, had the larger impact. Windows 7 is quite popular with consumers, selling over a half billion licenses thus far. However, the impact of tablets, and other non-Windows post-PC machines is not yet known; it could be that this decline in Windows revenue was directly caused by such devices. Alternatively, consumers could simply be scrimping on new hardware (that ships with Windows). Or this could just be a statistical hiccough.

If consumers are simply light on funds, the decline in Windows revenue means nothing; it’s instead a factor of the larger economic climate, and says little about the core strength of Windows and the larger PC market. If it is due to supply chain disruptions, then Windows is again unscathed. I want to posit that I deeply doubt that Windows 8 is, for now, causing consumers to hold off on purchasing new machines. The operating system has yet to reach its beta, and Microsoft has not said when it will be released. What consumer is going to hold off for several quarters in hope? Only a very technologically savvy one, and we doubt that there are enough of those to push Windows revenue down by such a substantial chunk.

Therefore, I would argue that if the economy, or Asian flooding are not to blame, we may have seen the first tremor at the foundation of the normal PC market, and therefore, Windows in its current form. In certain critical regions, the economy improved in 2011, making the decline hard to place squarely on its shoulders. I’m exceptionally hesitant to step this far out, but as consumers move to tablets, until the launch of Windows 8, larger Windows revenue could suffer as sales dollars move to iPads, Kindles, and Android tablets.

However, in all of this there is an obvious question: What happens when Windows 8 comes out, and Microsoft joins the post-PC movement? A Windows 8 tablet, employing an ARM chip and not running the normal Windows desktop (as has been rumored) is as post-PC as an iPad. This means that the most iconic PC OS could in fact make out well in the post-PC environment if it ends up being a competitive product. Therefore, Windows has to save itself from decline.

Windows revenue will likely grow in the next few years, even if Windows 8 is not a hit on tablets; this is a question of rates. If the most fervent believer in the idea of a ‘post-pc’ world is right, Windows still has legs to run as a multi-billion dollar business for decades. But whether it remains the core future of the computing world is the new unknown.

Will Windows 8 be a hit on tablets? For now Microsoft is sharing nothing new, so we are in the dark. All eyes on the upcoming beta then, on which a great deal stands.