Kinda like how iTunes was brushed metal forever while the Finder was Aqua and some apps roll their own UI to mimic Aqua? It's not like either Apple or Microsoft produce consistent applications, let alone the lack of control they have over third party developers. There is also Carbon vs. Cocoa, where different programs get different services "for free" from the operating system (e.g. spell check). Apple is just as guilty as Microsoft.
Giving a couple of decade-old examples doesn’t show that Apple is “just as guilty.” Apple has two toolkits: Carbon, a legacy framework for transitioning from MacOS classic, and Cocoa. Microsoft has releases a new toolkit/look-and-feel basically every other year. (Win32, WPF, Metro, UWP, etc.) And unlike Carbon, which is depreciated, Win32 is in active use by new apps and keeps getting new features.
There are a lot of different versions of Win32 and WPF based on the Windows and .NET version they’re targeted to, respectively.
Cocoa is more like targeting an evergreen browser. Just target the version that is just old enough to support enough users and you’re good (and users are happy). Unlike evergreen browsers, though, you do hit hard cutoffs once every few years, but I suspect navigating those means updating the compilation/signing process more than rewriting anything (correct me if I’m wrong).
I thought they'd more than deprecated it, and that Carbon apps won't run anymore on Mojave. They declined to do a 32-64 port all the way back in Mountain Lion.
The original discussion was about desktop operating systems but if you toss in iOS, how many look-and-feel changes does that add? Given the state of Marzipan apps that Apple thought were fine to ship, it may be ever more relevant. Apple didn't even replace the "slot machine" date picker from iOS which is horrible to use with a mouse.
Microsoft is the same as its always been but acting like Apple has a clear, unified, and sane design doesn't reflect the evidence.
Microsofts worst enemy, IMO, is their OEMs who are allowed to put all kinds of custom side-hustle garbage into the OS and it takes alot of work to remove it. Essentially, you have to pay a premium to a manufacturer to signal you're a "serious" user instead of "consumer" user, or you have to spend time removing spam... I mean "custom" apps that the OEM got paid to put onto your machine. At least, Apple only hustles their own ecosystem apps and let you safely hide or remove most of them.
Kinda like how iTunes was brushed metal forever while the Finder was Aqua and some apps roll their own UI to mimic Aqua? It's not like either Apple or Microsoft produce consistent applications, let alone the lack of control they have over third party developers. There is also Carbon vs. Cocoa, where different programs get different services "for free" from the operating system (e.g. spell check). Apple is just as guilty as Microsoft.