The menu.get method of the Menu service uses the Menus module's menu_tree_page_data function. This function returns a menu as it should be displayed in the current page. Some sub-items may be hidden, for example. As the notion of a "current page" is not relevant to a Web service call, I propose that this method uses the menu_tree_all_data function instead, which returns the complete menu tree, regardless of the current page. I believe this would be a more natural behaviour for this method.
