Not fatal but it opened the door for everyone else. If everyone was happy with the new Windows Mobile proposed in this article and it had widespread adoption, would Apple have developed the iPhone? They might have, but it wouldn't have been such a slam dunk.
They can still do a slam dunk ... the mobile market is big-enough for everyone to fit in.
Anyway, why in the world would anyone use Windows CE when there isn't a market for third-party apps on WinCE? What incentive does it offer for mobile manufacturers? Pocket Word?
That's what Apple (and also Palm and Nokia) did right ... delivered their own software, their own hardware, created a market for third-parties, delivered a decent design (personally I don't think it's revolutionary. it irritates me actually).
Hopefully Google/Microsoft learns from this. More competition is better for everybody.
Absolutely. They "almost missed the web" but then went on to have the dominant browser for over a decade. The history of Microsoft has been to let other people innovate. They did not invent the PC, the GUI, email, the web, the browser, spreadsheets, word processing or anything else that they now dominate the market in.