100 million units really isn't as "mainstream" as you think. A movie like last year's Pirates of the Caribbean 2 sold an estimated 64 million ticket sales in the US alone. Movies were about as old as home consoles are now when Gone With the Wind sold 200 million tickets in the US alone.
Of course that's not a fair comparison... But how about iPod... Apple just sold 21 million of them in the holiday quarter alone. That would be amazing for a whole year for any videogame system. iPod did 46 million on the year.
"[Our former customers] are unable to find software which they WANT to play."
"The way to solve this problem lies in how to communicate what kind of games [they CAN play]."
Satoru Iwata, Nintendo President. Only slightly paraphrased.