That said... porting to both OSX and Linux isn't that far of a stretch since OSX is Darwin Unix under the hood. The Kernels are different but the file structure and many of the libraries are similar. So they then get another OSX game on Steam.
Actually they both use OpenGl and that is the big bonus. The Kernals are both Unixish but the file systems and the file format are more different then it looks like under the hood. Glad that we are seeing the start of the end of Linux hate?