In EB Games, t-shirts promote video games. In Soviet Target, games promote t-shirts.
TLDR: A company called EGP Apparel, baby of Experimental Gamplay Project, is producing and selling t-shirts based off of indie games. With these shirts come free demos/copies of the game in question. That there blogger makes some points about how it's an interesting way to sell the games to a new audience, and quite possibly accurately targets a more interested ("casual") audience than just tossing the games up with the PC games.