We have looked at this issue extensively with the hope of producing a native version. We even looked at QT as an option. Using QT or writing the code directly using the Mac APIs would require us to re-implement our window handling, font handling, event processing, every dialog, every menu, and every tool window. While this isn't 100% of the code, I would consider this to be a "full rewrite" due to the magnitude of the change. Also, unless we selected the QT route, it would leave us with a version that is so different from the other platforms that many features and defects would have to be implemented twice.
You must have abstracted "window handling, font handling, event processing, every dialog, every menu, and every tool window" somehow for the Windows version, so how come its so hard to do on the Mac (using QT or otherwise) ?
By the way, Mac sales went up 50% in the last quarter compared to a year ago, and I suspect developers are leading the charge, because with the degree of Windows integration and compatibility provided by the Intel Macs (eg. Parallels, a $70 program with "Coherence" mode
http://www.youtube.com/watch?v=rN9jNNeEd98) the Mac is the best platform to run even Windows software !