I think there's some kind of miscommunication here. Charachters never change expressions in these shows? Is that what you're saying? I've seen a lot of shows, both popular and obscure, adn I've never seen one where a charachter never chagnes their expression, unless it's something intentional to make them seem more robotic(they usually are a robot/android in these cases), such as Yuki from Haruhi or Rei from Evangelion. Those two are charachters I've just realize never change their expressions, but its done on purpose.