That is the problem for the devs. Once a copy of disc is sold, they don't get money from that. 10 people can play that game, and the devs won't see their money.
With pc, its all digital. Any copy that is sold, will go to them. Downside is piracy. Their games are risk to a piracy.
There is no win for both of them. Only gamers win both these situations.
As much as I want to shit on used disc users, for not paying the devs, we have our own shit of piracy.
Sales for both of these devices, depends on users who buys digital, or 1st disc copy.