You are correct. In the woods, frost is not real common. The leaves insulate the ground pretty well, and then later, the snow provides insulation. There might be a little freezing in the upper inch or two, but not much beyond that unless we have a long cold winter with no snow cover.
As far as snow goes there usually isn't a huge problem UNLESS the snow is packed tightly around the trunk of the tree, which causes it to stay frozen at that level, preventing recharge of moisture in the tree during a freeze cycle. Usually a few warm days causes the snow to melt away from the trunk a little bit, forming a depression (or in Inuit/Eskimo -- a qumaniq), allowing the sap to be pulled upward (during a freeze) so the sap can run when it gets warm again.