This is more nuanced. You get in-game currency for skins/cards you already have in both Hearthstone and Overwatch, which is equivalent to being able to sell your cards
With hearthstone, can't you also "sell" any card you have for in-game currency, in addition to getting currency when you obtain a duplicate? In overwatch, you just get currency for duplicates (or randomly from a box).
I believe in Hearthstone, the only option you have is to turn the card to Dust, and then it takes so much Dust to craft other cards, based on their power and rarity.
