I could be mistaken about this but the night my CPU fan wasn't runninig and my processor got hot I went to the Intel site to do some research on safe operating temperatures. If I recall correctly, this is what I found:
Core2Duo processors can have temepratures read from a location directly in the center of the top of the processor (which also happens to be the critical heat transfer point to your heat sink). They also utilize one of the pins to transfer core temp data to the motherboard but not all motherboards support that option, thus the first method is also available.
Safe operating temps IIRC are in the 70+C range. There are failsafes built into the processor to help keep it below critical temperatures. As the processor passes normal operating temps it will reduce clock speeds to reduce heat. This process is supposedly almost un-noticable at the user level. If temperatures reach critical states (somewhere just north of 100C), the processor will cut voltages until it reaches safe temperatures again.
To verify this you can go to the Intel web-site. You are looking for a document on thermal management. Like I said, I might be wrong as I'm recounting this from memory but I think this is correct.
That said, my guess is that your and my motherboards are able to read the core temp data being supplied by the pin as they are both newer boards.
Using the stock Intel heatsink/fan/thermal grease my idle temp is ~27-28C and my operating temp under load is less than 40C according to the n-view monitor (I have an NVidea mobo) . Also, according to n-view, my CPU fan rarely runs over 1000 rpm (although it does on occasion). Normal fan speed at idle is ~990 RPM.
I'm not sure that answered your question but I'm reasonably comfortable that the temp readings are accurate.
