You also happen to be clearly not in the US, where the opposite is also true.
Very few serious shops only have pc's.
This would be similar to pro suicide. since most revenue in film/video is generated from AD agencies which are by in large 100% apple shops - except for the bad ones which invariably are windows based.
The great majority (51%) of US professional editors were on FCP by 2010 and 21% were on Avid products 70% of those were on Mac based Media Composer systems.
Since 2011 when Apple lost a lot of users in the FCPX debacle a lot of the bottom of the market moved to APP, but really the mix has still stayed in Apple's favor in this transition with most just moving to OSX based Adobe creative suite.
You are right that shops with render farms are not on apple systems, but most of those run Linux and not windows, and develop their own tools from open source ones. Wether you are talking about Weta/Pixar/ILM/Dreamworks/Rhythm and Hues/BlueSky, etc; even as these style shops slowly all fade into the past with the work is outsourced to overseas sweatshops using cheap pcs but with crazy amounts of cheap labor instead of big machines.
Pixar used to be all Solaris based before moving to Linux.
Before that most serious pro environment were completely Silicon Graphics shops until siligraphics decided to self destruct.
Today most pro work in the US originates/is created on a mac or is pre visualized on a mac and some of it ends up being finished on some os86 system not running osx.
Also sadly your statement about software's origin is pretty incorrect.
Having been a part of this industry since 1991, I can say without hesitation that the GREAT majority of professional content creation tools didn't originate on any windows platform.
Except for some of the much newer offerings starting in the late 90s early 00s --When most thought Apple was dead did they start developing for NT first, and even this was because Microsoft bought a bunch of those companies to castrate Apple & Silicon Graphics both of which had a strangle hold on content creation. Then when SillyGraphics imploded in what has to be one of the most spectacular examples of mismanagement did serious software like flame/flint/inferno/houdini etc; got ported to Linux and later NT and finally OSX.
Most serious media software has in large part originated from MacOS/IRIX/Amiga then transitioned to LInux>OSX>NT in the late 90s in that order. (mostly because NT was not made with media creation in mind and took some wrangling to code for at first.
With the exception of software created after 2002, like some of the more modern 3d software (Rinos/blender) or some of the modern compositors (Fusion) which where first NT based and then became OSX/LINUX ports.
AfterEffects for example only became windows based after version 3.1 for example and only because adobe bought cosa/aldus; and then first only for French/German because of low MacOs penetration in these countries, since they came to the graphic computing party late, and missed the initial Mac wave.
Premiere was always a MacOS product first, with a windows version missing most features, until 2003 after which it became premiere pro to compete with FCP because it was mad Apple bought it from Macromedia, before they managed to acquire Macromedia.
Avid, Digidesign, Autodesk, Media100; etc all originated most of their products on MacOS (not osx mind you) and then transitioned to NT* later with the market (although Autodesk bought a bunch of companies with DOS based products like 3DStudio which were never made MacOs Compatible)
More importantly 3d software and most high end compositors/color correction etc, where mostly IRIX based (Softimage3d/Flame/Flint/Inferno/Flare/Smoke/Lustre/Alias|Wavefront 3d tools/Shake/etc) then some were ported to Linux and some to OSX directly (because unix) then eventually ported to windows.
The reason OSX based transition makes sense is that its more synonymous to IRIX as it is a full UNIX system where as the DEC NT system that is the basis for all modern windows systems is a completely different beast.
The point of this very very long post is that in end the real advantage of a high end OSX based Mac, is that it's a standard X86 based intel system, that is built with higher quality components that typical mainstream pc's has better support then most mainstream pcs, can run every single modern x86 operating system either in bootcamp at native speed, or in a virtualization window; and is actually either at price parity or at cheaper price point then the SAME offerings from Dell/HP in their workstation divisions. (please don't compare a Mac Pro to a dell dimension doods, you can actually do a processor to processor match at this point)
So technically these apple systems are WAY more valuable then the standard HP/DELL workstation at the same price point which can only run Windows/Linux; and don't benefit from the insane price pressure apple is able to put on vendors... (Try to make a self made system with a Xeon and 2 FireGL cards and PCIe SSD for the same prices as a MacPro and watch your eyes melt from the real price shock. Try to make a Dell/HP/Lenovo system with the same parts and see what happens to your heart.)
*all modern windows systems which have supported content creation are NT not actually the lessor DOSWindows. (which ended with win98)