IMHO that is a fatally flawed analysis. You really don't intend to proove ubuntu won on the basis of search engine data would you?

The higher volume of searches can mean anything:

Case1: They might represent the popularity of the OS in which case, according to the second graph vista is far more popular than linux from 2007 onwards.

Case2: It might be that people were searching for solutions to problems as the OS usage increasesed....which I beleive is the cause for the jump in vista's popularity after 2007.