Google makes quite a bit of money and is extremely successful. I believe if they wanted to buy a country they would be able to do so without many problems to face because they most likely already thought of all of them. Google is a very smart company and should be able to buy one if they want.
While I am a huge proponent for capitalism, and enterprise, I do believe that if Google would purchase a country it would be an abuse and too far reaching for one company. I think they should just stick to the Internet which they seem to have mastered, and invest their profits into something Internet related. Buying a country would be way too far reaching.