not entirely true. Gnome has a first class language - Vala [1] - that is for writing performant system level applications. And the community is quite active as well - https://github.com/trending?l=vala
If you think of automation, there have been attempts at bringing flow based programming to the Gnome-JS engine (think of it as Quartz Composer integrated into the desktop) [3] - plus the fact that http://extensions.gnome.org is about as automatic as you can get to customize the desktop.
Is it a difference in positioning ? Because honestly I'm a little befuddled on why all the developers on HN get supremely excited about JS on OSX... and not something like NoFlo.js integrated into Gnome.