This one's a quick idea:
Magic swords in D&D are different from other magic weapons. In order to simulate this, for enchantments in my game, these rules are in effect:
Any weapon can have Puissance and Accuracy enchantments up to +5, and Penetrating Weapon enchantment up to (2).
Swords, after the first level of Puissance and Accuracy, must put a Bane on all further levels. In addition, they can have up to Penetrating Weapon (4) with the same Bane. All Banes must be for the same category of foes.
Further, only swords can be intelligent (and most magical swords of more than +1 are), and only swords can have more powerful enchantments (such as Dancing Weapon or Flaming Weapon, or others).