I got ahold of the person who has the underground pressure tank near Mazama, WA that I had seen. It's at a cabin used for cross-country skiing. The frost depth there is 5'. The pressure tank vault is 7' deep and includes the pressure switch. The installer said that he had done this for 17 years and never had one freeze or a pressure switch problem. That extra two feet was enough to keep the air from getting cold enough to freeze the tank.
The installer said he put a little grease on the electical contacts and that's all. Of course, the ground is drier on that side of the mountains. I'm still spooked about an underground pressure switch.
As to a remote pressure switch, here's what I've learned. The problem is with the loss of head in the pipe between the pressure tank and the pressure switch. If the switch is 100' from the pressure tank, and there are lots of couplings and 90 degree elbows in the supply pipe, and the pipe is only 3/4", and the pressure switch is 10 feet above the tank, and you're trying to run 6 gpm to the house, you've got a problem because of the loss of head caused by these things. Loss of head equates to loss of psi (2.31 foot of head = 1 psi), which can equate to inaccurate pressure settings.
Let's say the loss of head is 10 psi between the tank and a remotely mounted 40-60 psi switch. (This number is huge, but easy to work with). You have a pressure gauge at the tank and one at the switch. The bladder in the pressure tank is at 38 psi, 2 lbs less than the 40 psi cut in pressure.
But because of the head loss, when the remote switch kicks off the pump at "60 psi," the tank might actually have 70 psi in it, because it doesn't suffer from the subsequent loss of head. After the pump kicks is off, the pressure gauge mounted at the switch would continue to rise, showing that the system is equalizing somewhere between 60 and 70. Probably closer to 70. The gauge at the pressure tank would drop as the pressure equalizes.
When the pump comes on again at "40 psi," the pressure gauge at the tank might still read 50 psi. This inaccuracy effects both the drawdown amount and the pressure that you should have in the tank bladder. If your bladder pressure is set for the "standard" 2 lbs less than than the cut in pressure on the switch, it is set wrong. The bladder either needs to be set at 48 psi (because 50 is the real cut in pressure) or the pressure switch needs to be adjusted so that it cuts in at 40 psi at the tank. This difference in the pressure at the tank and the pressure sensed at a remote switch can be a problem. It can reduce your drawdown amount so that your pump is cycling. Just what the pressure tank and switch are supposed to stop.
You generally don't know and don't care about the minor differences in pressure caused by head loss thoughout the system. If you have 40-60 psi at the pressure tank, that's good enough for most situations. You don't care that the pressure actually hits 85 psi at the well head or that it actually is 31-51 psi in the third floor bath.
You can still have 40-60 psi at the tank with a remote mounted pressure switch if you adjust the pressure switch based on the reading at the tank, not at the switch. You can reduce the head loss (always a good thing) with larger pipe, less distance, fewer fittings, etc.
Most installers probably don't want to get involved with yelling back and forth from the house to somebody at the pressure tank in the yard. But I my research has shown that nothing bad, like water hammer, legionaire's disease, etc., is caused by a remote mounting of the switch. It's primariliy an ease of installation issue.