Disabling Default User Being Added To Main Site As Subscriber

If I understand the default function correctly, if a SuperAdmin creates a new user for a network site that user is also automatically added to the Main Site with the “Subscriber” role as the base default. Is this right?

Also, if a Network Site Admin creates a new user for their site in their admin, that user is also automatically added to the Main Site with the “Subscriber” role as well. Right?

In our setup, all new blogs (aka network sites) and all new users are being setup in the backend by the SuperAdmin —

So – is there some way to disable the function that adds a new user to the Main Site when that user is “created” in the backend?

Or maybe I’m missing something fundamental?

Thanks