Re: NVidia Thermal Monitor (Applet?)
Nvidia-settings retrieves its information from the NV-CONTROL extension which the drivers proivde. In the end the drivers read the info from the i2c bus but only one two types of chips are supported by it the LM99/MAX6659 and a builtin sensor (6600GT/7800GTX). NVClock on the other hand reads everything from the i2c bus and supports much more chipsets including the Winbond W87L785R which is used on your card. (it provides additional fanspeed monitoring and adjustments) Lm_sensors doesn't show any sensors because a i2c module for nvidia cards is required like the one from the rivatv project. Only this driver can't be used alongside the nvidia drivers.
Perhaps you also wonder why lm_sensors can't find the sensor and nvclock can. The reason is that nvclock can be seen as a driver in userspace. It accesses the videocard using /dev/nvidia* and then implements its own i2c layer using which the chips are accessed.