Obviously it would be a lot of hard work. Implementing a whole API on to Windows, but let's look at the advantages: - For starters with a few simple UI tweaks, all of the Mac App Store apps could run on Windows, giving them a decent base to work off of. Some would say "what's the point of owning a Mac then?" But I'll cover that in a moment. - If Apple could make it successful, what we would then begin to see is some developers building their software for Windows in Apple's API, in Apple's Objective C language and publishing it only on Apple's store! This is where it gets huge. Suddenly Apple has an ever growing piece of the pie on Microsoft's own platform. - Back to the "well what's the point of owning a Mac if all our Mac Store Apps are on Windows?" To reverse that, suddenly a load of Windows only software is on the Mac, with a few tweaks. Now this part, this exact part, is the biggest part of all. It's software that makes or breaks a platform. Just look at Microsoft's command line DOS, beating Apple's GUI based OS, simply because the Mac had jack all software. It's all about software (and price obviously, which Apple does not try and compete on at least in the low end market, but software is equally important). Whilst the Mac App Store is going to give a massive shot in the arm for Mac development, this would be much larger than that.