It has its own name.
An application may for instance say that it accepts any newer "minor" version.
For security patching you can replace a library with a new "build". So if an application uses libraries placed in WinSxS or the GAC it will pick up any centrally patched libraries without the risk of jumping to a too new version with breaking changes. The new version can exist alongside older versions and they can all be patched - for security reasons or otherwise.
A vendor can also distribute libraries alongside the application - in the application library itself. In that case the responsibility for patching is placed squarely on the vendor of that application.
No wonder everything gets so messy in the registry :)
That seems unlikely (i.e. can we upgrade the whole OS with NuGet?), but it does look like it is, at least, aware of some of the problems an actual package manager solves.
For development it's a different story, there you can have several levels of dependencies, but there NuGet at least appears at least as powerful as similar options on other platforms.