you are correct. The difference in the 2 apks is just branding.. the installer makes sure you get an EHS apk compatible with your current OS build.
I think the idea was partly to be sure you didn't have to be careful to install the right APK for the branding of your OS, simplifying initial installation -and partly to simplify re-installation after uprgading to a rebranded OS.
Persisting the installer over an OS upgrade would allow you to re-run it after upgrading to a rebranded OS, and get an EHS apk that matches your new, rebranded OS. Then you should be able to install this EHS version in place of your old one, make it the default launcher, and reboot - the new EHS version would use your existing EHS configuration file and you would be back in business relatively simply.
of course I am leaving out a few details .. but I believe that was the intent.