Making games requires creativity and a great game idea is an important part of that. However, starting a company need more than just a great game idea. If you are looking to go the digital download/self publishing route you also need to know how to market your company and your games to customers and how to effectively seperate them from their cash.
If you are going the publisher funded start-up route then you need to understand how publishers do business, how they make purchasing decisions and the processes they go through before making the final “buy” decision and how that impacts on your buisness. Publishers don`t buy good ideas, they buy the whole package of an idea combined with a team capable of actually getting the game made. That means that before starting a game developer you need the idea, the people to create it, an understanding of the development process, an understanding of how publishers work and knowledge of who you need to be talking to.