|The temp readings in the bios have been tweaked in the bios's code such that they're quite accurate for the particular mboard model. |
Third party hardware monitoring programs make assumptions about the sensor readings that may not be correct for the particular mboard model. You can usually tweak the settings in the third party program so they match or are close to what the readings in the bios are.
Sometimes sensors for something are not connected to the intended inputs on the hardware monitoring chips - the mboard manufacturer compensates for that, but the third party program doesn't.
The third party program may show a reading for an input no sensor is connected to - it never changes in that case, and may even be an impossible reading.
Asus's own Probe hardware monitoring program is usually quite accurate for Asus mboards. If you have the CD that came with the mboard, it's probably on that for you to install.
Or it can usually be downloaded from the software downloads for your mboard model on the Asus web site.