I think Maxime is pointing out that there are two ways to configure the service – both are perfectly valid and they perform the equivalent operation:
1. When the msi is installed, enable a certain feature on the msiexec command line (or use the interactive gui) to install the service
2. Use the chef-service manager binary that now ships with Chef 11.6 (actually some earlier versions as well).
This PR from Julian uses #2 – this is actually good since in order to do #1, you'd have to invoke msi and have the msi properly installed. It's possible (though unlikely) that you don't have the msi available or that it is corrupted, so the operation would fail if you tried to enable the feature. It would also be somewhat slower. The chef service manager binary was included for lightweight configuration of the service that did not require going through Windows installer, scenarios like this one.
So to answer Maxime's question, this approach is independent of installer packaging and does not require invoking a package manager – if it at some point we used a different packaging for Chef on Windows, this approach would continue to work. Additionally, it is faster and more lightweight – it won't hang if some other software is being installed by Windows Installer at the same time, for instance.
Serdar who authored the chef service manager binary may have other comments as to why this method was chosen beyond what I've covered.