he's not saying "don't make casual games". he's saying "don't limit yourselves to your definition of 'casual' games".

don't think to yourself "i'm going to make a casual game as opposed to a AAA game". make a game designed around your skills and desires, and built around your resources and attention span.

is it the typical lastability, price, development time, or what that makes a game casual? if you make a game that'll last longer than your typical casual game but is much cheaper than a AAA game and sells somewhere in between, what type of game did you just make? or do you even care?

julz