Think of the first time you ever used a computer. I agree that once you know that there is a app called terminal, using the Hierarchical menu might not be the best way to launch/use it. But the very first time you use a computer, its useful to see "Ahh - I can do Graphics, Programming, System Administration, Games. Oh wow it even has Solitaire!". So a hybrid approach with something like Gnome-Do for power users while retaining the hierarchical menu for regular users is optimal imo. Heck a lot of power users even create application sessions and do most of their app launching automatically at startup.