In terms of revenue Google will sustain for ever, they may or may not have earned what Microsoft has achieved now, but their Growth is always exponential and continous. Microsoft will saturate at one level.
May be they know that when they initially released Windows thats why to avoid saturation they are releasing new new version. Patience of the customer or consumer how ever you call is limited, nobody wants to keep changing their working platform. Even myself I'm moving to UBUNTU 10.04 today as my XP crashed 2 days back.security lapse. I will not recommend this for others now. you must have basic knowledge on Linux before migrating in to it if at all you want to.
I would say survival of Microsoft windows is a question in future, very soon consumers will realize but it will be atleast 2-3 years. (my guess)
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