Clarke proposing navigation using geostationary satellites as beacons in an idle thought (which is more analogous to EGNOS) is not the same as inventing GPS, and is not the same as building a revenue stream from it.
Details in http://dvice.com/archives/2010/07/arthur-c-clarke.php
Steven Johnson's TED talk has an entertaining and slightly more accurate take on how GPS was invented.
http://www.ted.com/talks/steven_johnson_where_good_ideas_come_from.html

Doctorow has never let mere facts get in the way of his rhetoric. 