The day windows OS died?
"Regardless of whatever new products arrive, Microsoft clearly no longer considers Windows sacrosanct."
This is an important observation. Office on iPad means more symbolically for Microsoft than in practice. Sure, Office on iPad options are great for fine-tuning and will make the Office experience more fluid and democratic via cloud services like Microsoft OneNote and/or Dropbox. That's a good thing.
But on a deeper level, Microsoft is absolutely minimizing the relevance of the Windows OS, the consequences of which we'll see play out in the next few years. But it had to be done, and big kudos to Nadella for bursting Ballmer's reality distortion field bubble.