[sebazzz]

> Doubly so when Microsoft themselves don't use it

Often, as you mentioned, Windows Installer packages are wrapped by an executable (in WiX this is called a "bundle" because you may also choose to add redistributables like the C++ runtime).

However, what you see in installations like SQL Server, Office and Visual Studio is that the installers are bundles as well - of a large amount of MSIs that need to be installed and uninstalled in a specific order. A single Microsoft Installer package is transactional and can be rolled back on failure, but bundles are not as well defined and left open to the implementation of the bundle. Windows Installer does not reach beyond the single msi package.