According to this site, the MKIV and 1JZ motors came with metal head gaskets.
http://www.jza70.com/articles/engine...omp_chart.html
That would be one factor.
The common head gasket failures with the MKIII's are due to lack of torque from the factory.
They really should have recalled them!
It does not take that long to tighten up the headbolts, but instead many MKIII's seen the junkyard instead of what could have happened....
EDIT: by the way, is there a reason why you posted this in the MKIV section?
Were you trying to get the feedback from the MKIV'ers and their take on all this?