Well, Pryce's entrance is tailored to get him applause. It's the end of the song and he's just revealed.
With the rest of the actors...more so Norbert and Joanna at this point, it really comes down to one person. If one person starts applauding when they come out, then the crowd follows. People just are unsure if it's appropriate to clap in those entrances, so that one person needs to start it. Lack of applause for Norbert probably just means there wasn't one person to start it. At this point, most people know who he is, and have heard great things about his performance I would think.
Greeneyed, Lucie Arnaz is taking over for Joanna. I'm assuming you saw Rachel de Benedet go on for Joanna? I agree she's great, but overall a tad young to take over the part fulltime.
"If there was a Mount Rushmore for Broadway scores, "West Side Story" would be front and center. It snaps, it crackles it pops! It surges with a roar, its energy and sheer life undiminished by the years" - NYPost reviewer Elisabeth Vincentelli