Ashton 9,
Being from East Texas I never had thought about the fact that in the North, the ground freezes down several inches in the winter. You are probably right about more caches being buried in cellars or somewhere in the house in the North than in the ground. I have found only two, what I guess you would call, caches. One consisted of 154 Memoirial cents that were evidently buried by kids in a yard in the Dallas area. the other was 984 coins (mostly cents) that, the best I can figure, were pumped from a wishing well, along with debris, onto a hillside in Arkansas. I'm not sure that these qualify as true caches as we picture them but I guess they are close. Yes, I believe that logically thinking, caches were probably meant to be dug up by the owner over and over as he or she needed to take out or add money. That means that it would be buried fairly shallow (probably no more than 12 inches). The owner would need quick access so as not to raise suspicion. Those of you who have recovered objects at a foot or so know that even that is a fairly deep hole.
Also, don't overlook the fact that, at least here in the South, we have what is referred to as a "posthole bank". That is where a fence post was left loose from the wire in a fenceline and a jar or a long metal box was dropped into the hole to hold money. It made for very quick access and was almost undectable. I'm still looking for one of those!
Good luck,
BRD