This is a great analogy. Many business ventures have unforeseeable risks or are based on conditions that may change dramatically from day to day. The thing is to manage these risks by saving extra money and by diversifying as much as possible.
Now personally my family business is diversified into web publishing, real estate sales and home construction. Unfortunately the real estate and construction markets have tanked here and this time of year is when we normally see most of our real estate/construction revenues so the July 27th update really hurt as we were already suffering from other "legitimate" businesses doing very poorly.
So any business model has serious unforeseen risks that one needs to try to be as prepared for as possible. Building a business model on free search results is just as legitimate and no more risky than farming, commercial fishing, real estate, oil exploration, etc. With any of these endeavors the bigger you are the better you are able to issolate your self from short term down turns.