Marketing is any action that affects the perception of another so as to change the probability of making a sale. Rapport is part of that perception. To put it in simple terms, part of marketing boils down to whether the client likes you. Naturally, this affinity by itself is not enough to make clients refer their friends if they are not convinced you deliver good legal services. However, lack of rapport with your clients can cause them not to refer prospects to you even if they perceived you did a good job on their matters.
Most attorneys pay little attention to rapport building.
I've had more than one attorney tell me they are running a law practice not a popularity contest. Some even think that having a good relationship with a client is detrimental because it clouds their objectivity. This is short sighted. As competition for clients gets more intense, this kind of attitude will lead to an erosion in their client base. Competition changes the general perception of the market.