For any operating system to be considered for home or office use it needs to be compatible with other platforms and stable. Why would anyone choose to use an operating system that required a massive investment in support just to keep it from crashing and losing critical data?
Mac OS X was built using technology found in a version of Unix called BSD. While UNIX is itself over 25 years old, Mac OS X has only been available for desktop/client since 2001 and has been gaining strength and a wider user base since then. While old and reliable is nice, Apple also made it possible to hide the sometimes scary Unix aspect under the elegant and very stable user interface that we recognize as Mac OS X today. But stability isn’t the end all and be all here - we also need to be able to read and write documents of just about every type without hassles. We need our communications to be written, received and used by anyone without hassles or compatibility issues.
For such document-specific support, major software companies have stepped up to produce fantastic software and updates with features found only in the Mac OS X versions of their offerings. Among those companies are giants like Microsoft with their MS Office suite, IBM has Lotus Notes, Adobe with their Creative Suite, Quark still actively develops good old QuarkXpress and there are many others out there too numerous to list here -- so sharing that Excel spreadsheet from your Mac with your colleagues who are using Lotus Notes and Microsoft Office 2007 is a cinch. Or perhaps your mom took some pictures with her pocket camera and sent them to you from her PC and you want to do a little do-it-yourself retouching and send them back to her. Not a problem!