Is there some reason to use two widgets rather than one?

["Tom Liu" <tom.liu@xxxxxxxxxxxxx>]

Hi,

            In Gtk, looks many widget can combine to one.

For example

            GtkHBox and GtkVBox.

            GtkHScrollBar and GtkVScrollBar

            GtkHSepartor and GtkVSepartor

            ………..

Why not combine it with one widget and use one properties to change the style?