Re: sounds familiar
I can't speak from internal knowledge, however I have developed software (large scale) on both platforms. I can honestly say from experience that Mac OS (pre X) APIs were amazingly difficult to develop for in C and C++ compared to Windows (even 16-bit). This generally was because Apple never bothered to add APIs for many tasks and also because when they did, you often had to spend ages searching through header files for functions since documentation was terrible at best, missing in most cases.
An example would be a simple task of changing a window title. You'd write code in assembler to wait for the CRT refresh, then alter the memory location of where the fixed length window title was stored before the screen was redrawn. This was the officially unofficial way of doing it because there was no API to change the title after the window was initially created.
Probably the biggest job involved in transforming NeXT Step into a Mac OS was development of the Carbon API which finally made full APIs for app development on OS 9 and later OS X. It was insanely difficult because the old Mac OS code was so littered with pre-object oriented APIs and other legacy garbage. Even the simple concept of a message loop didn't exist in the old OS.
OS X was a nightmare for developers since the good APIs were off limits from a C application and nearly impossible to reach from a C++ application. ObjC could call C which could call C++, but it didn't work well in reverse. This was solved around 10.4 or 10.5, but until that time, companies like Microsoft had to write Carbon applications because otherwise they wouldn't be able to reuse code from their other platforms.
If I were to speculate, Microsoft would probably have Mac versions done before Windows versions because they had 1/10th the features. No COM/OLE, no scripting, no support for apps like Visio, no publisher, etc... Office for Windows was just had many more features which had to work. Office for Mac was used mostly by individuals where Office for Windows was a business application.