RG:
From what an airline source/Malaysia press conference previously released:
(1) They do not appear to have the sattelite option for ACARS, using the VHF option instead.
(2) They apparently did not exercise the "Boeing tracks our ACARS" option in their support contract with Boeing.
Some pages back, a PPRuNer provided
a map with a series of notional, overlapping VHF range circles and ground station locations to give an idea of where you would expect to see ACARS(VHF) be able to receive data from an aircraft in flight at cruise altitudes. You can see that there is a bit of a gap west of Thailand. IF, as also discussed in this thread, the RR data system only sends info when something changes, as opposed to "every x number of minutes," then it is very plausible that no message was sent until the plane was in that gap, IF that gap is where it ended up. As you can see, there is a lot of "IF" going on there.
Beyond that, no comment on why Uncle Sam thinks the bird went down in the IO.