another member, Colt357tw who agreed to be quoted, was at the IDF in Taipei this year where Intel stated about 20% of (secondary) heat losses goes thru traces and passed over to PCB and surrounding components on their 875P models
Jim then asked right away if Intel can provide these type of tests for their partners(motherboard makers) since hooking up over 30 thermal couples on an ATX motherboard and 8 more on the IHS is way too much work for any motherboard makers, even 1st tier ones like ASUS, engineers would kill themselves try to gather meaningful data from run that type of testing.
the Intel response is not known.
the Asus twist can be seen
here
but the addition of such a plate could boost that percentage considerably
the same old reason to use a heat die