If the Legacy crew had some reason they really wanted to change altitude then they would have asked. They flight planned at standard altitudes and would have had a view ATC would move them around to suit ATCs plans. This might or might not have included ATC descending them at Brasilia.
So that being the case even if the flight plan with the pilots predicted a descent to FL360 they would not have to ask for clearance to descend from their current altitude (FL370) to FL360.
And Then ATC would not just have to give clearance but would have to ORDER the descent and try to contact the pilots.
So ATC really plays a significant role in this case. They have to monitor whether or not all flight plans are being followed accordingly. It is their sole responsability.
So if you are right I would have to agree that the pilots are not to blame for not seeking ATC clearance (if they didnīt try that)
