MG23: I was at the ICAO meeting when the MoU was signed between the US and ICAO at the end of the 90's. the clause was there.
Since then there has been in 2007 a declaration during an ICAO assembly by a US rep that said :
Today, on behalf of President Bush, I am pleased to announce that the next generation of GPS satellites (GPS III) will deliver signals without any compromise in precision -- guaranteed. That is because the United States will remove the "selective availability" capability from that system. Eliminating this source of potential uncertainty in GPS performance for civil uses will make the system even more attractive to the world's users.
The reasoning was at the time that the US could not accept that " forgein hostile forces " use GPS to guide weapons aimed at their own troops.
This clause was also used to obtain funding for Galileo in Europe.
As far as I know ( and I welcome if someone here can correct me( the clause is still there. Everybody hangs on the 2007 declaration but GPS is still owned by the US military ( although managed by a joint US military/ civil body)
Interesting is what is written on the gps.gov web site FAQ :
The United States has no intent to ever use SA again. To ensure that potential adversaries do not use GPS, the military is dedicated to the development and deployment of regional denial capabilities in lieu of global degradation.
Hopefully you do fly an Embraer in a potential "Regional denial part of the world " .