I think that's a pretty reductive stance to take. Keyboard nagivation is more productive _if_ the primary use of the tool is text-based. In a word processor, an IDE, a file manager, or anything else where the primary mode of interaction is reading, typing, and processing the things you've read and typed, keyboard navigation can be demonstrated to be faster and more natural _only if_ the user has taken the time to learn the shortcuts.

For tools that are mainly for non-text visual information, then the keyboard versus mouse debate is much more heavily weighted in favor of the mouse. Even then, there are times when effective keyboard shortcuts are far more useful than menus and icons. Take any CAD or 3d modeling software as an example. 90% of what a user does will be interacting with visually-presented spatial data, but even then knowing the shortcuts for changing tools or modifying a tool's settings will make you much faster and remove the need to constantly navigate nested menus of options.