While Tinderbox is a one-of-a-kind-tool I think it can be discussed if it is underpriced as some people believe. As a mac user I am hesitant to use an expensive tool that isn't Cocoa. Sometimes there aren't any alternatives, but that is not the case in the thriving outliner market.
Why is Cocoa so important? In three words: look and feel! I'm suprised that a company that is aware of the importance of texture and sensuality for writing and creativity makes no attempt to use Cocoa in their software. If you sell Moleskines and handmade italian leather journals why not use the corresponding electronic user interface?
Also the reluctance to port Tinderbox to Cocoa makes me wonder about the future development af the mac version of Tinderbox in view of the planned Windows version. I get the feeling that my $165 (not to mention the yearly $70 for updates) will be used to develop a windows version which will further reduce the likelyhood of a Cocoa version.