People who have had lobotomies can have a serene look on their face also, but that doesn't mean I want a lobotomy...
JWs usually look happy before and after the meeting when they're socializing and talking about things unrelated to being a JW. But during the meeting, some are asleep, others are bored and some are daydreaming of being somewhere else...those are the ones who look happy during the meeting, lost in their daydreams.