If the trees were well watered just before ground freeze, the trees
should be fine, the watering is to keep the
roots coated in water so they don't freeze (think of oranges and other fruits that are sprayed with water mists as the air freezes, it is done so the fruit is coated and thus protected).
Conifers are always looking for water to bring into the tree, so their water needs are, as Mike mentioned, more demanding, also their roots tend to be closer to the soil surface than those of deciduous fruit and nut trees.
Redhawk