Mothers.
Mom says to her son Jake, "Okay Jake because you have been such a good boy, I will buy you your favorite game". With much enthusiasm and careful studying behind the glass cabinets Jake proclaims, "I have found the game I want. After hailing a Wal Mart employee mom uses her credit card to make the purchase. Jake can hardly wait to get home so he can be the first one on his block to play this new game that he decides to get a head start and read the instructions on the ride home.
If it were not for the hardcore gamers and the fans that pay retail prices for games, the market would shrink.
As for Joysticks and gamepads versus the keyboard, there is a large selection of games I would rather use a keyboard and mouse. Obviously PC games like Sim City and First Person Shooters require the use of a keyboard and mouse but it is so much better to play Diablo with a keyboard and mouse. You need to program your number keys for selecting magics and items on the run or die unnecessarily.
4 bit and all the way up to first generation Playstation games can be played easily with a keyboard and with a little dexterity and practice you can perform Ryu's fireball as easily as if you had a control pad, although in that case I would still prefer a joystick or a game pad.
Atari, NES, Genesis, Turbographx 16 were made for the keyboard in my opinion.