Ornis:
This doesn't quite make sense to me: asking for something DCA claims existed. And why would Acars be via satellite where VHF was available?
They're asking ICAO to examine a 'standard' for the real time tracking of aircraft. That is something that does not currently exist. There are systems available that can track aircraft outside radar coverage in real time, such as ADS-B/C, however only a few ATC centres have the capability and not all aircraft are equipped. Airline aircraft routinely transmit position information and engineering data via ACARS, but that information is not used to 'track' the aircraft in real time.
In the case of MH370, the aircraft had the capability to transmit its position via ADS-B and ACARS. However, that all stopped when the transponder and ACARS both stopped transmitting. I guess an ICAO standard would have to require an independent system that can't be tampered with or disabled by anyone onboard the aircraft.
Regarding the second part of your post, it all comes down to cost and availability. In some areas the airline's provider (SITA or ARINC) may not have the necessary VHF coverage, and in others (e.g. Japan) it is actually cheaper to route ACARS messages via satcom rather than VHF.