There is a lot of research and psychology underlying the answer to your question.
"News" and "gossip" (divorces, layoffs, etc.) are information-based. The "impact value" of the information being passed along is essentially the same (the first time someone hears it) whether that person hears it from an actual observer or from a friend of a friend of a friend. It spreads quickly because a sizable percentage of U.S. adults (30 to 65 percent, depending on the topic) have a psychological need to be the "first to know" something, and the "first to tell" someone else.
Business "word of mouth" is a somewhat different dynamic because it's based on an
experience, not a piece of information -- and for someone to be psychologically motivated to tell someone else, it has to be an
unusual experience. The "impact value" of an unusual experience can be high if the person talking about it is the person who experienced it -- but unlike information, the value of an experience declines exponentially with each degree of separation between the person who experienced it and the person who is talking about it (most people don't care what a friend of a friend of a friend experienced, unless it is the stuff urban legends are made of).
The more unusual a business experience is, the more likely the person is to share it. Unfortunately, "bad" unusual experiences happen to customers more often than "good" unusual experiences. Socially, many of our acquaintances respond to us better when we talk about bad experiences (they secretly like it when we have to struggle or encounter a problem -- only our loved ones want to hear about how great everything is going for us!). So people share their "bad" experiences more readily.
There are at least three types of "good" unusual experiences that have a chance of spreading via word of mouth.
The first is an experience that gives the customer an unusual sense of power or control (an example would be a car buyer who believes he totally nailed the negotiation and made the dealer give him everything he wanted -- he'll tell people about that).
The second is an experience that entertains, amuses, inspires, or touches a customer to an unusual degree (Pike Place Fish in Seattle is often used as an example of this -- people tell other people about experiences like that, and those people often pass it along).
The third is an experience that is
radically better than the customer expected, and significantly better than anyone else is offering (for example, if someone started selling gasoline for $2.00 a gallon at lunch today and continued through the afternoon, the resulting word of mouth would probably get them on the evening news tonight -- lots of people would tell lots of other people quickly).
Creating word of mouth is largely about creating an unusual positive experience for customers -- an experience they'll be motivated to talk about.
