Time machine was built to solve a very real problem:
Eighty percent of Mac users said they knew they should backup their data. (This is scary already. Only 80 percent?) Twenty-six percent said they do backup their data. That actually doesn't sound too bad until you get to the next question. Only four percent backup regularly.source
This is not some weird geek issue for sysadmins, but a profound fracture in how people use computers. With that user focus (4% regular backups!), Engineers worked to do something about it. Windows users probably have similar backup rates, and yet the technology developed was never exposed to the majority of its users. Power users often ignore the UI as irrelevant (bah its just eye-candy) but the way features are presented to users is critical, as VSS so clearly demonstrates. Apple engineers worked both on the underlying details, but also a UI that works. I don't think VSS had any such user focus, it was probably built as an IS feature. No one at Redmond had the bright spark to allow normal users a clean way to use it too.
So why don't we use it more - because the UI is clunky, its only in explorer and and once again, other apps don't take advantage of it.
OS X is cleanly built around the idea of unified interoperable thin frameworks. Services are offered by the OS and used by applications. Applications are encouraged to allow interoperability by offering exposed dictionaries of things they can do to any application that asks. Developers are encouraged to use such unified services. Tom Yager expresses it this way:
Windows and Linux are designed from the core out, which is to say that they are all about layered kernels, system calls, and APIs, with each layer's purpose being to abstract the layers below it. The layers grow thicker; when a layer gets unmanageably thick, a pretty new abstraction layer is created so that people don't have to deal with the ugly one. ... Everyone plugs into OS X through the frameworks, and below that lies a stable, thin, simple, and well-documented system stack. It is not the frameworks' job to abstract lower levels of software. From a developer's point of view, the frameworks are OS X. When developers write to Apple's frameworks, they inherit cross-application integration and operational and interface consistency with no effort. source
Even before Leopard came out, the main apps I use had added support for Quicklook! I think quicklook is more clearly thought out in UI terms than the various preview mechanisms available in several versions of windows back to 95. The proof is in the pudding
; and that is that Quicklook will be a core UI feature for most users whereas Preview has been available but woefully underused on windows.
Spotlight *is* a good example of this. I used X1 / GDS on my Windows machines before my forced move
to OS X. So I was fine with a windows equivalent and it was a useful tool. Yet because Spotlight is a core OS service, and cleanly exposed in a framework, many of my applications use it. That makes spotlight far more useful for me as a user. Developers can all build on it and it just becomes more valuable to users as a result. Vista now has a search mechanism (though a much less robust metadata framework), but what is a developer to do when there are so many other possible search services to support (and most users are still on XP)?
In conclusion, the two examples you give are fairly clear cases where an attention to interoperability, user focus, and cleanly exposed frameworks benefits both developers and users.
As I've not installed Leopard yet I've not been able to compare its functionality, but just reading through the Ars Technica review, Time Machine is actually more advanced than VSS as far as I understand. One can recover individual items within a file store, for example a deleted entry in an address book, or individual mail. VSS would force the user first to know what the file name that stored the info was, but then restore would lose all changes made subsequently. It would require manual hacking to get the data out. Selective item revisions without data loss is a critical feature of a backup system, and thus technically VSS could not provide such complete functionality even if the UI was reworked IIUC.