Microsoft doesn't have very many resources compared to what Linux (and even Ubuntu) does. There are more people who use Linux than any other operating system in the world, and more developers working on it than on any other software project in the world. It gets more eyes and sees more development.
If there's anything for Microsoft to be worried about, it's that: you can't buy that level of active development. The work that goes into the Linux kernel alone takes thousands of developers around the world and manages tens of thousands of changes to the code every day. No company could ever do that on the traditional level.
That's what Google means: they've been figuring out a few ways of harnessing some of that extraordinary power for enterprise. Microsoft still works hard and turns out a good product, but I think there's a reason they have to pay so much more and work so much harder to develop something that is still perceived by the market as mediocre. You say the switch to 'enterprise' software is unavoidable - but Google, one of the largest and most successful companies of our time, recently dropped 'enterprise' operating systems in favor of their own version of an open source operating system when they made the decision to say that employees couldn't use Windows unless they got manager approval.
Having market share over document formats and things like that will preserve Microsoft's position for a while, but how long? The fact is that development on the old model - behind closed doors, by a team hired by a company, specifically for company goals - has been shown to be slow and outmoded. The companies that are really succeeding now are companies that realize this.