They are comparing the totality of the value something has been bought for. So a $60 game needs to sell 10 copies, when $600 piece of hardware just needs to sell one. That’s been the reason why Valve Index was nr 1 for so long - it was very expensive, with purchases comming from the enthusiast market. Same thing for the steam deck - not many people will buy it, but it will be worth a lot of AAA games.