X11 may not be the default windowing system for OSX, but it's been available since OSX's inception. Also, Darwin is not FreeBSD, even though it is based on it. You need to compile everything from source to make it work (this is the definition of non-trivial). And lastly (albeit most importantly), Apple hardware is comparably priced with anything from Dell, HP, or Lenovo (check it out). That being said, if the author wanted a retina display for whatever reason, he needed to buy a MBP. The other manufacturers you name don't offer products with this high resolution.
My first laptop was an ibook G4 which I bought second-hand, just to see what the fuss was about. Although I had the same opinion of OSX at that time, I was wrong. It took me about a year before I jettisoned OSX in favour of Debian (and later Ubuntu, when it worked well enough). The hardware, though, was fantastic. I've since owned several laptops and none have outlasted that old ibook, which is still in use (it's our kitchen computer now).