There are three ways to 'scale' a computer program. The first is optimizing the algorithms and data structures which is discussed in the section you noted. Make your code run as fast as possible using a single thread even when the amount of data you are processing gets extremely large. The second is taking advantage of better hardware (more cores, bigger L2 and L3 caches, SSDs, etc.) which includes spinning off threads to do single tasks in parallel. The third is a 'scale out' architecture where the application is spread out across multiple machines.

With all the cloud infrastructure available today, too many programmers focus on the third option (which can mask inefficiencies in the first two) when they could get as good or better performance at a cheaper price by focusing on the other options instead.