The casuals are important because they buy a system for one game or one type of game. Wii Sports and Wii Fit were the games that drove Wii and Kinect Adventures was the game that did it for Kinect on Xbox 360. On Nintendo's front, the casuals were a powerful force because Nintendo was able to make a fad out of Wii and were able to get people to buy into those two games. The same applies to a lesser extent to Kinect and Kinect Adventures.
HOWEVER... does this make casual gamers a huge unstoppable force? No. It makes them a quick and easy revenue driver, easy money. They come, they buy, they fall silent once they've bought it.
The core gamers on the other hand come, buy... STAY and continue to buy. They don't just stop at one or two games, the average core gamer will buy a large number of games, invest in the system, buy the DLC, pay the money for the premium online experience.
When you've convinced that core audience to buy your system, you're ensuring long term success of your system. When you've convinced casual gamers to buy your system, you're thinking short term. Look at Nintendo right now, at Wii U. It has a HUGE problem right now in that it's not attracting casual gamers. Why? Because Nintendo hasn't turned the ownership of the system into a fad as they did with Wii. That mass market appeal they had isn't easily transferred from Wii to Wii U because that casual audience has alreayd bought that one system with those one or two games, why do they need this other device?
Unfortunately for console manufacturers, they can't sucker customers into the yearly refresh that Apple and other smart device manufacturers like to do with phones and tablets. The way the console gaming industry works doesn't allow for that kind of marketing and as a result, the casual audience that buys into that kind of marketing ends up being a lesser player in the grand scheme of things.
So yes, casuals are the silent majority, hardcore are the vocal minority... but casuals don't spend as much money on this stuff as the core audience does... and when it comes down to it, this isn't about being heard with your voice, it's about being heard with your money.