This is not the USDOD GPS. This is Inmarsat's DGPS service that provides ~1-2cm accuracy. Which, if you're driving between rows of produce can be the difference between harvesting or crushing crops.
https://www.deere.com/en/technology-products/precision-ag-te...
With DGPS corrections, like you get with the satellite that failed, you get about 10 cm positional accuracy. For dryland crop farming, that's often good enough. It is more accurate than what most human operators can achieve and reduces operator fatigue. So many ag GPS systems are setup to use it out of the box.
There are other solutions, in addition to RTK. Trimble has "CenterPoint". There are Omnistar corrections (different sats, better accuracy than DGPS). Novatel has "GLIDE" but I've never seen it in use.
$100 ublox module + accoutrement https://github.com/taroz/TouchRTKStation