Every magic item in the D&D Essentials starter adventure comes with a power card. Or a magic item card, I guess: none of the magic items (lifedrinker greataxe, darkleaf leather armor, magic staff, chainmail armor, bag of holding, amulet of health, 2 potions) actually have a power. None of the cards are marked Common, Uncommon, or Rare, either.
Would it be convenient to have a card for every magic item? I guess it would be fun to get cards as part of getting treasure. Also, returning cards to the DM is a good way of tracking the use of expendable items. Still, sometimes my party goes into a dungeon loaded for bear: everyone buys, like, 5 potions. Where are we going to get 20 potion cards? (Hmm, 10 Essentials Starter sets, only $130 on Amazon!)