It's interesting to read comments about this today, written through the lens of the present. I suspect many commenters were too young to really understand the level of dominance Microsoft had in the market circa from 1995-2005. Just look at this chart:
https://www.extremetech.com/computing/143277-microsofts-shar...
In 2004, outside of education and desktop publishing it was extremely rare to see an Apple computer at all. Apple was the iPod company by that point. Almost all software of note ran only on Windows, and Office was required for all documents.
That Microsoft is dead, killed off by antitrust remedies and the web. That today Microsoft is a giant company is irrelevant...it's not the same company at all. In fact, there is no company today even fractionally as dominant. Google's search monopoly or Apple's App Store monopoly just don't compare.
It appears all the critical commenters think PG was unaware of these facts, but they critically misunderstand the truth on the ground. There was no way for PG to not know that Microsoft was dominant everywhere because Windows ran everything (even digital signage) and Word documents were a more accepted interchange format than even PDFs. He was invoking Gibson's observation that the future is unevenly distributed, and he was right: The movement of almost all applications to the web absolutely annihilated Microsft's ability to dictate what software smaller companies could or could not publish.
Edit: Also, it seems unthinkable today, but back then we all had a large number of devices like printers and digital cameras that only shipped with Windows drivers. Microsoft essentially dictated what hardware you could buy too.