From what I've gathered, some GPUs don't have a VRM temp sensor or at least one that sends a signal outside the card. I have the Sapphire HD 7870 and it gives me the same sensors as OP in GPUZ and HW info reports the same stats. I had an MSI HD 7870 for a while as well and that read out VRM temps as well as a myriad of other temps and currents, voltages, etc. It depends on brand, essentially.