While that statement is technically true, it is a bit misleading. One skill will not add 1% to their current DE nuke damage, but 1% of their normal (non-DE) nuke damage. So if you have 400 Divine Magic skill on PLD, 16 more will only increase the total damage by 4% compared to an unmerited nuke.
Each MAB, on the other hand, will add roughly add 1% of your current DE damage to your nuke (assuming a MDB neutral mob and 0 native MAB). It's a simple matter of diminishing returns, which are quite high if you consider that your base is already at 400 (PLD's Divine skill caps at 404). So the approximation of 1% damage per 4 Skill is accurate enough for these calculations, or to dumb it down further: 4 Skill = 1 MAB.