He notes that a blockbuster game normally has a blackout period of a few weeks, meaning that when a new game comes out -- he uses Halo 4 as an example -- there's a period before and after its release when gamers are less likely to buy a similar game. Whenever that same game gets DLC, players are once again less liable to purchase a similar game for a certain period before and after the release of the DLC. After all, why would you pick up Call of Duty: The Next One, if you're still playing that fancy new Halo DLC?
The long and short of it, says Divnich, is that DLC has nothing but a negative impact on retail. It's actually a double impact, as DLC both prevents gamers from buying a new game and from selling their current games back to used game retailers like GameStop. According to Divnich, digital sales are going to seriously impact retail sooner than believed.