I'm pretty introverted, too, but I never felt very pressured by my parents to do things. I did things my friends were involved in or that I thought I might like. But I think you're right in that Duncan himself wasn't an introvert, and we see that later in the season. It really is a change of behavior for him due to Lilly's death (and, you know, what he thinks about his relation to Veronica).

I really don't like the Kanes for the most part, especially Celeste (admitting, again, that I did like Jake sometimes because he can be nice to Veronica), but I can occasionally see their side of things. :)