Innovation!
The technical innovation came from the PC manufacturers who 'cloned' IBM PCs by reverse engineering IBMs BIOS and thus producing a mass market that fell into Microsoft's lap. The only innovation Microsoft brought to the table was by screwing IBM non-exclusivity and repackaging some-one else's DOS as their own work.
Oh, sure it was innovation, it created a big monopoly from Microsoft over all the hardware makers, so Bill Gates could be the richest man on the world!!!... I don't know how somebody can see it as something innovative, that created the hegemony from Microsoft. and even with their failures many people don;t have any other option but to use Windows, even if they don't like it... and even Mac has done a long way to make easier to choose, to use MacOS with most of the different applications, or even letting you to choose hardware and/or OS, there's still too many people that doesn't know this.
And by the way, yes, de GUI MacOS, when was recently released... of corse it had to be for one company at that moment! How could somebody create something new, so innovative and let everybody take it without the advantage of makeing deals with the companies interested on that OS!? That's what Microsoft made because they didn't invest developing, they just copied MacOs, that's why they gave it to all the hardware manufacturers with less cost, and that's why the hardware companies took it.
For example: iTunes, and of corse the iTunes Music Store, had to be just for Mac at the beginning, and once established as the best of his kind, they extended to Windows. That's the logic, the all-manufacturers way to make things.