It is not that hard do build-in a count() method, but what should it return? It is a collapsable list (each item can have sub items). Should it return the top level count? The count with all the sub items included?
Perhaps if there was a list.count() returning top level and list.count2 returning all items. More fully, if those methods were available on each list item then you could get the counts at every level of the list as needed.