Apple was at a point in the late 1990s where they HAD to innovate, or die. Their series of fiascos with clueless CEOs and never-materializing products (Copeland) had pushed them to the brink of collapse. Microsoft has not yet had to face such a challenge, perhaps they will and emerge a reinvented, reinvigorated company like Apple, or they will continue to stagnate and eventually be another Wang in the history books.
This is why I think we shouldn't count MSFT out. They've had it so easy for 10 - 15 years that they have turned to competing among themselves for something to do. Once a real sense of fear and external competition sets in we may see a very different beast.
EDIT: typos