In the same way that developers that focus on specific aspects of a game (Story, AI, etc.) get better with said aspects, companies that focus on certain game Genres tend to make them better. So, a company that has a lot of experience in the Action genre would have learned from previous experiences and would most likely make a better Action game than a company that’s focused on Strategy.
Just my two cents.
Feels more like companies that specialize in a genre just get good at not producing something terrible. Companies that have produced a dozen action games aren’t likely to produce anything innovative for their thirteenth game. It won’t suck, but it’s not going to break new ground.
You already specialize in genres by virtue of your team makeup. If you stack your employees with higher tech skills, your company will be more able to produce Action/Simulation/Strategy games. That said, rather than a flat bonus to game quality for a certain genre, I’ve advocated that more experience with a genre should allow you more flexibility with the sliders. A company who has mastered the art of the action game can tinker with the fundamental building blocks of the genre and still get away with it game quality wise simply because of their experience and familiarity with the genre.