It really seems to come out in the wash that way. We have the concept of use ( and ) to group stuff beaten into us from an early age. Then you can either choose to separate elements with , or with nothing at all. It makes sense that the first element is special. Then you can nest them. And that's it really. How else would you do it? Lisp is the "it's code by default" model and Forth is the "it's data by default" model.