I would guess the 'do enchantments fade' anon made the line between charms and enchantments at "charms is an item made to be a spell" (like charmbags, put together only for spell purpose) vs "enchantment is adding magic to a previously existing item"
Ohh ok ok.
I would guess that the charms would fade less quickly, because of my beliefs of how magic works.
Enchantments would be more likely to fade quickly, again, based on my beliefs.
But it still depends on your skill as a practitioner and how you prepare either object.