You're right that ICAO cannot impose the rules. However, by being a signatory to the Chicago Convention, states are obliged to either comply with ICAO SARPs or file Differences. Either way, states concerned are responsible for ensuring compliance with their own regulations.
A quick gander through the US AIP (GEN 1.7-23) gives an idea of their filed differences. I don't see too much of the verbage previously quoted being a notified difference.
Perhaps the question should be directed at the FAA as far as standardisation is concerned?
http://www.faa.gov/air_traffic/publi...bs/AIP/aip.pdf