Somewhere I recall reading that the fire problem is caused by fuel lines cracking and then leaking diesel. On GE engines the fuel lines are external to the block and the leaking diesel eventually encounters something hot enough to set it on fire. On EMD engines the fuel lines are internal in the engine block and if they crack the diesel dilutes the crankcase oil which will eventually cause other problems, like maybe crankcase explosions.

Kind of a "Damned if you do, Damned if you don't" situation. I suspect that it is much more complex than my simple explanation.