Vista IS huge, that tends to happen when all of the new computers sold come with it preinstalled........
I dont think there is a huge amount of people running out to the store to pick up vista.
Exactly. Vista/Xp is really huge simply due to OEM sales when you buy a computer. MS will obviously not tell people this, but I bet that retail sales of Vista are near zero of make up a minute percentage of OS sales in total.
Microsoft has done a great job distributing their software. If they didn't, they wuldn't be the giant they are today.
They sell well because they are (or rather have been) the only real choice of OS's by the public. Part of this was the point of history when Apple nearly went bankrupt. The cloners (which MS doesn't compete with) ensured that computers blanked the market.
Another thing is that Microsoft goes way out it's way to accommodate business needs in whatever way they want to - a business method that directly opposes Apple's philosophy. Consider how much we know about Windows 7 (which has been leaked and talked about to death my MS) compared to Snow Leopard (very little detailed about it beyond screen shots). Thats despite the fact that Snow Leopard will probably go out to sale before Windows 7 will.
Microsoft's devotion to businesses ensures that companies buy Microsoft software en masse. Sales to enterprises are huge in size when you look at large companies. These trickle down to consumers who buy Windows out of sheer apathy (they don't know anything else), work compatibility (or that they use Windows at work), or for some special purpose that they cannot get from Apple or Linux like a home server (I know that Linux does this, but Windows is still out there and Apple is not) or for gaming (very minor on the Mac due to graphics limits on consumer devices, and nearly non existent on *nix system).
The vast majority of windows purchases are when you get a computer or by enterprises with volume licenses. Upgrading with retail does happen, but the whole debacle with Vista Capable proves that it doesn't goes well all that often. The whole Vista Capable mess was just so that people would keep buying computers and not wait for Vista.