> If you build for Motif it looks like Motif. If you build for > windows it looks like windows.
Not looks, *acts*. Motif has quite a few requirements about how the menus should be laid out, which mouse buttons do what, hotkey layout, etc. Cross-platform toolkits usually give you different looking menu but with the exact same set of actions. If you isolate the GUI, you could have different GUIs with different *interactions* not just different appearances.
