Because that is what they do. Intel TAT reads it directly off the chip, most motherboards infer the CPU temp from a cheap sensor in the socket.
Jokester
The sensors on the core aren't exactly callibrated either, but it's the best we've got.
I am currently running at 3.3ghz cpu voltage is 1.33125 is that good.
Only in your head.
Tho it will add a few milimeters to your e-penis.