[Skarg]

It seems pretty clear to me that the rules intention is that skeletons do not decay.

An explanation might be that yes the Zombie spell enchants what is there to enchant. Enchanting the flesh of a zombie has the major advantage that damage will not shatter it like happens to skeletons, and the disadvantage that for a year or more, the rotting flesh degrades the enchantment.

The spell is not able to enchant just the skeleton inside the corpse. If someone researched such a variant version of the zombie spell, I might allow it but treat the flesh as armor and assign encumbrance equal to the flesh weight (100 - 200 pounds, maybe giving armor 1 and -1DX per 50 pounds or so).