In fact it is a legacy from the cold war, to achieve the greatest precision the US located most of the GPS ephemeris over Moscow(In fact when we study cases of best GPS reception we call it the "Moscow case") So the Russians being very upset about the gps constellation invented hand held jammers, the story priced these jammers 150 US$ in the streets of Moscow.
The majority of the ephemeris may or may not be over Moscow, I don't know and I've not seen an authoritative cite that they were.
What I do know is that no US ICBM does or did use GPS for primary guidance. First of all, it is not needed. Inertial guidance with terminal phase radar guidance is extremely accurate. Secondly, as you said, GPS signals can be jammed with a USD 150 device and no ICBM would be risked by such a trivially defeated system.