Like kowen said, it's still a (STABLE) *nix OS, but with a beautiful, functional UI.<p>RE: "Or is it that Mac developers are more vocal about their OS beliefs?"
   The question you should be asking is what makes Mac developers so vocal about their OS beliefs?  I think the answer you'll find is that they are so pleased with their Mac they feel compelled to share.<p>There's also a handful of fantastic development tools unique to OS X, two of my favorites being TextMate (RoR editor of choice by many), and Coda.  There's also obviously been large growth in Objective-C developers since the release of the iPhone, again something (unless you count mono) unique to OS X.