It doesn't. A trained tech can do all 4 pads and rotors in 30 mins or less.
The "book" (Chilton is most common) is an industry standard time study. They publish times that an average technician, working with hand tools, would be able to complete the job. All shops, stealerships, and shadetrees can use these times to remain competative simply applying there shop rate to the Chilton book hours.
For jobs such as this brake job, dealerships will often drop their hourly rates, yet pay the tech the chilton falt rate hours knowing that they will beat the chilton time by far, allowing for higher overall daily efficiency, and being competative with the Meineke's (17 year old apprentice) rate of $50 a flat rate.