No, not necessarily. Depending on the level of granite or marble and the particular company or pattern of quartz; granite can be a significantly more cost effective material. However, if you are considering a level 3-4 granite/marble, or an exotic stone; quartz is most likely going to be the more affordable way to go.
Some factors that change the cost of granite are the extraction of the stone, and the shipping of the material which consumes a lot of time, money and energy. Factors that change the price of quartz are company, pattern or color of material, demand, labor rates, thickness and edge treatment, among others.