It looks as if the inspectors were pinned down during the pre-iOS7 period of rather obtrusive and ornamented (baroque) UI which shaped the first OF2 re-skinning.

( If you look at the video on http://www.omnigroup.com/omnigraffle...-omnigraffle-6 you can see that the OG6 inspectors started off with the same flickering mouse-over ornamentations – concealing disclosure triangles – as OF2 draft 1 )

Perhaps Apple's move towards foregrounding workspace and data (and making UI less self-promoting) will now facilitate a clearing of the OG6 workbench, with inspectors moveable to adjacent monitors.