There's never been a "standardized" way to port games, especially when you're not using a virtual machine like Java or .NET. When compiling spits out different results for each operating system, problems will occur. There are ways of simplifying the process, of course. Using OpenGL instead of DirectX means you're building upon a graphics framework that doesn't have to be ported. And since the Mac now uses x86 CPUs, there's a lot fewer problems that can arise from hardware differences. It all comes down to whether or not the developers left themselves room to build for multiple operating systems. DirectX is very attractive, as Microsoft has sunk a lot of money and effort into making it work well and have a large feature base. OpenGL doesn't have nearly the same investment made in it, despite being free. Of course, given that CiV doesn't need the latest and greatest in graphics like every new iteration of the FPS genre, OpenGL could suit its needs perfectly.