About a month ago a conversation was going on here on the subject of myrk giants deaths.
First off - Normal myrks, being just as old as myrk giants, have a normal death sequence, which counts out the "old age" theory. I'm guessing the story behind it is the fact that the myrks are saturated with magic, tearing them apart at death. (the magic being the force allowing their skulls to explode - if they were normal munitions, don't you think they'd have a limited number like satchels?). That raises the question of who gave the myrks their magic ability? The giants are described as slaves in their decription boxes, not creatures in a position of power. Was their some kind of shaman ruler in ancient myrkridian society?
On the other hand, we have the less glamerous reason for their weird death sequences.....
Due to their size, like trow, if the giants fell all the way to the ground, instead of just collapsing - It would look rather weird, esspecially on steep hills. It's hard to make a 12ft sprite lying horizontally believable =)
This is also why trow and FG's freeze then fall into little itty bits.