An interesting title, you might think – but there's a closer comparison than you might think. In Why VRML failed, Elliotte makes the point that without support for a minority platform, the whole benefit of ubiquitous compatibility was doomed to failure. It didn't really matter if that was 1% or 5% or 10%; without covering all the major platforms, supporting only two of them was a poor decision. Opera and Firefox survive because they recognise that in order to provide a better experience, they have to provide a native version for Mac.
The other item worthy of consideration in this is that the Mac is the second highest commercial operating system in the world. As a result, if you have a product on which you need to make money, Mac users are more likely to have the concept of paying for software instead of downloading it for free or being present in the distribution. As a result, software tends to be better on a Mac, because if it wasn't, people wouldn't pay for it. People buy products like OmniGraffle and Delicious Monster both because they can afford to, and also because they are high-quality applications with attention to detail (such as when you import a Harry Potter item into the latter, a voice whispers "Voldemort").
In the Linux arena, free is the default. No-one expects to pay for it; if it's not free, no-one's interested. And if it's not FreeTM then someone will write their own version with a far worse interface and claim that it's “better” simply because it's more customisable. For example, the classic “this is what happens when you let developers create UI” demonstrates the point admirably. And this was just a simple command line tool; compare that with the commercial Cocotech PathFinder for elegance.
Anyway, this brings me back to the point of this post; subversion. It's the next de facto standard for version control on the internet, and yet you can't download a current version for the Mac. The open-source subversion.tigris.org site has a downloads link, but the site doesn't actually host them; rather, they're provided by a number of volunteers around the 'net with no real idea of where they come from. Worse, a number don't actually host binaries; the Mac page claims that the packages are part of fink, but actually the last binary was SVN 1.2, and the other Mac sponsor is metissian, who haven't updated it since SVN 1.3. Meanwhile, CollabNet are providing 'certified' binaries, but only for Windows and Linux platforms.
Most Mac users aren't C developers. It's not like a version control system needs to be specific for developers at all; storing documents, using the WebDAV sharing remotely, web developers who want to version control their website, or even other developers working in scripting languages like Python or Perl, or even compiled non-C languages like Java or C#. Mac programs just come in universal downloads; they install with Installer.app (or, for a single application, just copied from a DMG).
Anyway, it's clear that subversion is distinctly a third citizen on the Mac, and that there's no interest in supporting it with a certified version any time soon. (CollabNet did not respond to this question when asked over a week ago.) And so, as a platform-neutral version control system, it's following the same path as VRML did.
Lastly, it's also worth noting that QuickTime is going down the same hole; given that Apple only support Windows and the Mac (but not Linux), is it any wonder that Flash has taken over for video on the web? It may be inferior in terms of video quality, but it doesn't come in a crippled pro version and it's available on any OS. However, QuickTime isn't going anywhere soon due to its central nature as libraries on Apple Mac OS X (including the Apple TV) as well as a key component of the iTunes picture. Just don't expect to use it for video.