Visual Studio uses MSBuild. csproj/vbproj files are MSBuild files. MSBuild will take an SLN file as an argument and do the same as Visual Studio would do with it when you load it and click build.
That seems like an inaccurate description of what's happening: http://stackoverflow.com/questions/11932164/what-parameters-...
They're using MSBuild, they just don't know it.
Given the age of projects I've worked on, and that it's unclear whether MSBuild is involved in VS's C++ compilation, I don't think your assumption is correct.
The change was explicitly to make it so that a C++ project file was an MSBuild script.
Visual Studio absolutely uses MSBuild for C++ projects.