OK the tweet doesn't make it clear whether Laura is referring to people leaving early at the bows or specifically at the end of Will He Like Me, I think.
If anyone here has read Richard Schechner they will be familiar with "transformational theatre"; Peter Brook talks about "holy theatre". I'm afraid PThespian I cannot reduce live theatre down to the level of the financial transaction you do: drama should be a shared experience and a communication. If the performance is working and the actors are bringing truth and their humanity to the stage, the audience should be there to do likewise. A situation where audience members basically say, "yeah the show was great and I ought to be honest enough to acknowledge that, but actually I'm a bit selfish and I just went to get home as quickly as possible so screw you", debases and devalues the experience. And for those who are scared of being crushed by the crowd leaving the building- just wait and let the others go ahead at the end of the bows, maybe stick around and listen to the playout, or ponder what you have just seen. All this, of course, if you thought it was a good show. If it's not you're thing, I'm all for leaving at the interval even.
As for the not-clapping after a ballad- I think Laura may be wrong. I've worked on 'She Loves Me' and that number sometimes lulls the audience into a cozy and happy state, but there is no real button to it so it's quite easy for the moment to pass without the audience knowing it was an applause point. One other thing: perhaps the director could look at whether this moment is pointed up enough to make it a clear button- is the lighting right? Is the blocking finale enough? Such things come into play.
I really hope Laura isn't such a diva that she demands applause even if audience members haven't been brought to that place. I can't believe she is.
I have no sympathy with those who leave early at the bows