Which was a feature in games before WoW but isn't a pay to win mechanic as you can not pay for "drops". WoW for the longest time refused to have a real money gold shop as was more that people were buying in game gold from 3rd parties anyway so might as well make a safe way to do it (which isn't a direct cash for gold transaction, more that another player has to buy your game time token, but that will usually happen within 30 mins).
As for hearthstone I would lay the blame more at Magic: The Gathering Online personally (though not the first), but I see you point that the game has very popular and became the "cardboard crack" that IRL Magic was (Atleast with Magic: The Gathering Online you could trade / sell your online cards with others until you piss off WotC and they nuke your account).