There are absolutely antitrust issues with grocery stores - Kroger/Albertsons is being contested right now! It's a major contributor to food deserts. It's not a cartel because the main players aren't acting in concert, but they are attempting to monopolize regionally. Walmart has also concentrated way too much power, but that's the 800 lb gorilla no one wants to touch.
That said, gas stations and grocery stores deal in commodity products. The video game companies are much more integrated with many games that will only run on one system, stores will only run on one type of hardware, and games are not transferrable between competitor systems. Competition is extremely restrained because of these exclusive and limited distribution agreements. The fact that they all maintain the same line on prices is a very clear signal of cartel behavior when you take the context into account - they are using control of a distribution chokepoint to control competition and pricing power. That's the essence of why antitrust laws passed in the first place.
That said, gas stations and grocery stores deal in commodity products. The video game companies are much more integrated with many games that will only run on one system, stores will only run on one type of hardware, and games are not transferrable between competitor systems. Competition is extremely restrained because of these exclusive and limited distribution agreements. The fact that they all maintain the same line on prices is a very clear signal of cartel behavior when you take the context into account - they are using control of a distribution chokepoint to control competition and pricing power. That's the essence of why antitrust laws passed in the first place.