While there are hundreds of reasons for this, the most important and fundamental reason for its success has been providing relevant information to the general public.  The problem today on the internet is not lack of information but the problem is information overload. Google scans through the billions of pages full of clutter and brings us, within a few seconds quality and relevant information which saves our time , money (lots of free stuff you can find with google if you can type in the right keywords) and energy. These are the three valuable resources which we try to build and save for ourselves. This is a significant problem that google solves and if someone asks the question how does google earn? the answer is'nt through ads but through delivering this value to its surfers. Yahoo had its directory in which it listed quality websites, but surfers were too lazy to type in the yahoo directory address to find quality and relevant website. This is what google recognised and identified the global surfer user need and fulfilled it.

At all times there are market situations where a certain need is not being met. This is what entrepreneurs do wheather online or offline. The reason we dont see many google's around is that it takes patience to build up the business model and putting in public benefit derived from the problem your business is solves before you think about the making profits .

The irony is that businesses interested in their work and aiming to solve a particular problem of their target market get a lot of money even when they dont ask for it. On the other hand, people and businesses that aim for money day & night and that is all in their mind, often end up broke and frustrated the only reason being that they were only interested in how many $$ they can make.

While a wish to earn more and more money is nothing wrong in itself.  But surely thats not the way to set up a successful business. If only money is your only focus you got a lot to loose in every economy and if money after delivering value to your customers ( in which you are genuinely interested ) is your focus then you have a lot to gain in todays dynamic economy.

Inspite of the efforts of google trying its best, still the problem remains to a certain extent. If today anyone can device a better and more effective  method to solving this information overload problem, I cant see any reason why they cant go ahead than google.