The article leaves out a lot of important details (it’s the LA Times, so that’s to be expected). The key predecessor system was NRL’s TIMATION, which used atomic clocks on satellites at mid altitudes (8 hour orbits preferred). GPS uses 12 hour orbits. See my article http://www.thespacereview.com/article/626/1
Great article Richard!
You know your stuff :-)
The time warping effects of the Earth’s mass also have to be calculated for precise GPS data to be had. The clocks on the sats actually are fast compared to the clocks on the ground...their speed slows their clocks down, but not enough to make up for the ground clocks closer proximity to the plant mass...the mass slows time down relative to the farther away sats.