The issue is that even once you have removed Launchpad from the Dock, when you install an app via the App Store, it opens Launchpad. I don't use MAS that often, but when I do, I get the truly awful Launchpad appear.
The last time I saw this a couple of minutes ago, I couldn't remember how to dismiss it. After a few seconds, I worked it out, as one would expect, but it prompted me to try to find a way to premanently disable it, or at least stop MAS from opening Launchpad when it installs an app.
This is how I found this discussion, and yes, I still find this iOS type feature an unnecessary aberration on OS X.
There is no MAS Preferences dialog to enable this behaviour to be turned off, so I was hoping that some terminal 'magic' might do it.