Has anyone already come up with this principle?
If I understand it correctly, the Qwerty keyboard layout was designed for mechanical typewriters to slow typers down, because fast typers would jam the typewriter. When computers came along and jamming was no longer an issue, everyone already knew qwerty, so the inefficient layout was preserved (in contrast to, for example, more efficient layouts like Dvorak that nobody knew).
So the Qwerty Principle would be, usability doesn’t happen in a vacuum. If people are already used to a paradigm that is “unusable,” that fact may itself make the paradigm actually more usable, as compared to alternatives which are theoretically more usable.
You can see this in OpenOffice. Because everyone is used to MS Office, OpenOffice mimics MS Office’s poor/confusing menus and dialogs. GIMP could probably benefit from this by more closely mimicing Photoshop’s keyboard shortcuts.