A number of things really...
Having a handheld powerhouse that can run current gen games (cut to res and mostly 30fps, but there has to be a trade off) that can also be played on the TV. This concept is more of a selling point for multiplats than often given credit for.
Proper marketing
Zelda at launch
Proper marketing
A steady release of exclusive games
Proper marketing
Mario and Xenoblade for thw holidays
PROPER FK#$% MARKETING