I think a good way to think about good design is the Einstein quote on mathematical models, that they should be "...as simple as possible, but no simpler." Normal mode in vi/vim is necessary for that program's goal of keeping your fingers on the center of the keyboard as much as possible: forgoing the use of arrow keys means that navigation and editing have to be separate modes. It's more complex, but only because it has to be. CSS on the other hand seems to introduce a whole lot of accidental, unnecessary complexity.