Not actually true.
Xamarin Studio is a branded build of MonoDevelop trunk - a bit like Chrome versus Chromium.
All the new Xamarin Studio changes are Free Software, and available right now in MonoDevelop git, and work fine on Linux (Xamarin Studio is still GTK+2, even on OSX)
Well, I guess I got all worked up over nothing. Even the article said Windows and OSX though and left out Linux, so I almost felt like this wasn't phoronix hate spin for once. It seems disengenuous for them to leave out Linux as the target of their development studio when developers are by far the largest workforce users of GNU oses.
Xamarin Studio, however, is just a badged version of MonoDevelop 4.0 - like Chrome/Chromium. And MonoDevelop continues to work fine on Linux.
What the hell this article has to do with Linux???