It is not clear how widespread this problem is. Maybe it's just a small fraction of units with the RAM slots accidentally overvolted or something like that. I wish more people could run memtest (Rember) for a couple of hours and post their numbers.
On the other hand, people are complaining about hot laptops all the time and the new Mini may be worse at least in the sense that the power brick is inside. Notice that the RAM sticks are almost touching the PSU box.
In terms of the sensor accuracy, as I said earlier, when the sensor shows 65C, I can barely touch the chips - that's about right. When the sensor says low 50s, it is still hot to the touch but I can hold my finger indefinitely - again certainly not way off.
Another case of Apple sacrificing function to form? Well I'll test it hard in the return period....