Yes. Thats because they dont have any cares like Arwen, Melian, and Aredhel. When Ebe and I work on these, we work on expressions as well.
For example, we are discussing Celebrian right now and we both agreed that she should have a sad expression because its the Fourth Age and her children are in Middle Earth.
So, there is a lot of thought that goes into these. Aredhel is suppose to have a thousand sad memories ...because as time goes by, it takes it toll on the elves.
Arwen is sad because well, you know...the choice that she had to make. Melian is smiling...thats because she is very sociable and hides her feelings well. :)