A company that develops and publishes video games

Actually you could check on Activision, Electronic Arts, Konami, Sega, Microsoft, Nintendo, Ubisoft, Sony and Namco-Bandai websites. They publish games for small studios, but all these companies develop and publish their own games.

Maybe the confusion is that they have several "campus" that are offices in the end, so for example, a game developed for Konami Computer Entertainment Tokyo (KCET) and published by Konami, is the same company that makes and publish the game, Konami.

Same happens for studios purchased by companies. As example, Maxis is a branch of Electronic Arts(EA), because it was brought by EA several years ago. So despite Maxis made the Sims, the studio is just an part of EA.