

Already Rhapsody had official support for two types of applications: applications for Mac OS running under the Classic (Blue Box) environment, and applications written using the Cocoa (Yellow Box/OpenStep) API. This is similar to the Windows ecosystem because Microsoft emphasizes backwards compatibility, some users could be running Windows software conforming to different UI standards based on when those software tools were written. The problem with having NeXTSTEP and OPENSTEP applications run unmodified in Rhapsody or Mac OS X is that users would have to deal with applications designed under two sets of UI standards. Apple is famous for its UI guidelines, especially back in the Classic Mac OS era. It's also the little details, down to the order of the command buttons on a dialog box. It's more than just the differences between NeXTSTEP's grayscale theming versus the Platinum theme used by Apple at the time. Come to think of it, the other problem with providing a NeXTSTEP/OPENSTEP binary compatibility layer is that the UI guidelines for NeXTSTEP/OPENSTEP and Mac OS are different.
