Windows Operating System was one of the mostly used OS for browsing internet. In 2010 no one would have agreed to with your claim that Android operating system will become the number one OS used to browse internet. Although as the current position Windows still holds the number one position as 38.6% users still use Windows OS for browsing internet. Android is on number two positions with 37.4% users. Android is quickly closing this gap.
With the current pace it will only take some months and Android will become most widely used operating system used to surf internet. You will get the idea by a quick look at these figures. In 2012 Windows held 82% global internet usage shares and on the other hand Android has only 2.2% shares. In last five years due to increase in smartphone use, mostly Android base phones their is only 1.2% difference in Windows and Android internet usage shares.
Asian countries are the major contributors where internet usage has increased and mobile data is becoming more accessible. If you take Chinese market for example 51.8% users are using Android OS for browsing internet and only 29.8% users use Windows operating system. Similar trend can be seen in India and some other Asian countries.
Apple iOS is the third largest operating system which is still far behind with a total 12.99% users use it for internet browsing. There is no doubt that Windows is still number one operating system for desktop and laptop computers. But tablets and smartphones are becoming a popular medium used to browse internet.