[Chris Crawford]

Interesting! It IS in the Preferences dialog -- but I failed to see it. That's because the label on the radio button is "Inspect a tool". That is shorthand for "set the Inspector to display all options associated with the selected tool".

This is a beautiful example of one of the trickiest problems in user interface design. Designers are so close to the work that they take for granted lots of things that users might not notice. And once a user has figured it out, it seems obvious. The problem is that some users -- like me -- might not figure it out. This is truly a killer problem in UI design and I think that the OmniGraffle designers made a small misstep here. Had I been the designer, I think I would have gone for a more verbose label such as "Update Inspector to reflect selected tool" {with click | with option-click}. Moreover, I would have added a tooltip explaining what that means in greater detail.

But UI design is a very subjective matter.