Quartz timepieces are more precise than automatic timepieces, which are spring-powered, but are far less intricate and detailed than automatic timepieces.
Quartz (left) vs. mechanical (right)
Source: http://www.watchco.com/watch-guide/quartz-automatic/
Essentially, 4G spectrum is more efficient at delivering data, so to download the same YouTube video, or what have you, it takes half the effort compared to 3G for the wireless provider. That makes it cheaper.
Source: http://readwrite.com/2014/05/09/4g-3g-smartphone-data-price-difference