It's widely known Google is bashing Microsoft with free version of on-line office suite, as well Apple with free Android platform. All that is possible due to a huge leverage of contextual advertisement revenue covering Google's expenses of free software development.
The contextual advertisement is the cash cow of the Google. All other services and software it gives out for free (almost). Sometimes that free make starving cash cows of other companies, like Microsoft and Apple mentioned above.
Thus, Office suite and Windows are money cows of the Microsoft, not the contextual advertisement. Why doesn't it give out contextual advertisement for free, at least for clients bought their software or for keywords with minimal bids?