Do you remember the tabbed toolbar thing that was once born in Kexi? It's an attempt to optimize the UI when collection of actions depends on context. This part of development goes well, even while there is no framework for use by other KDE 4 apps. Those still use the KDE 3 technology, i.e. KXMLGUI leading to rather big menus.
What's understandable many users prefer to use menus, and even more of them would ideally use both toolbars and menus. Certain actions are hard to express using icon or icon+short name.