The trait theory certainly does have its limitations, Kenneth. Traits interact with situations, and some people who are under-expressive during in-person conversations do find themselves feeling very freed up in the more anonymous cyber conversations. Digging a bit deeper into the layers of personality dynamics, we then ask WHY that's so.
It might also reflect individual differences in cognitive style. Some people may find the written word a better way to express themselves than the verbal word (hence poetry and literature).