Let's look at it this way!
If the US or Australia shot MH370 down then they had the legal right to do so especially if MH370 went through an ADIZ and failed to respond to Military CTR. It's thousands of miles from its planned route so no one and I mean no one can say a thing about it.
There is no justification in dreaming the most elaborate cover up ever conceived and pull the wool over so many stakeholders and I don't think either country will give a damn about any public opinion, especially from the Kafeneio. They have ADIZ for a reason.
Both countries would even shoot down their own if they had to.
And let's be very clear. MH370 was a lot closer to Australian ADIZ than Diego Garcia. Harold E Holt is a submarine HF communications station for the entire Australian Submarine Fleet and the USN Nuclear Submarine Fleet. That is where the launch codes are sent through to the USN ICBMs - not kidding.
http://en.wikipedia.org/wiki/Naval_Comm ... ld_E._HoltMH370 would most certainly be shot down if it got anywhere near Harold E Holt because if that place is taken out, the Australian and USN Sub Fleets are literally sailing blind.