Let me attempt to help clear this up. I may get lucky, who knows?
First off, Shia posted a comprehensive installation topic right around the time Win7 had been released and been perpetuating into the community here in NWN land. Though it had a great deal in common with Vista, there were still some additional layers of security that needed to be attended to, specific to the Win7 OS.
But...
Look at the date of Shia's original post and then the subsequent replies and additions. GoG was just beginning to offer Diamond copies and at that snapshot in time reports from GoG Diamond version users were not expressing problems when patched via the GoG v1.69. Again... this is over 4 years ago, folks. Shia's sabbatical began so the instructions have been pretty much set in concrete until her return, if ever.
However, since that time there have been an increasing number of performance issues with users of the patched GoG Diamond version. Much of this is due to drivers not supporting the version of OpenGL needed to run NWN smoothly, some basic graphic tweaks like disabling Shiny Water et al., and dealing with multicore systems, more prevalent today than in 2010 by far. It was a bit later that the BSN community began recommending that the GoG Diamond be patched with the Critical Rebuild and in many cases (not all, obviously... technology change is a continuum, much to the chagrin of the owners of legacy games which were never designed to operate on contemporary platforms) it improved performance.
Now Paul is noticing that even users who are getting good performance are allowing the Diamond version to be installed in the Windows directory like most software does by default rather than hung off the main drive partition. Well, actually, Paul... this is nothing new. First time NWN game owners have been doing this for years, way before GoG was even a fly speck of an idea. I can see how it could frustrate designers who base its correct functioning on the basics like proper installation. But PLEASE... calm down. You'll rupture your truss and we need healthy, physically-able, sane designers as we venture into the second decade of NWN advancements.
I will assume that this same topic has been posted on the GoG forum (haven't checked myself). If so, I would suggest filtering out the exasperation aspects (including the sophomoric topic title) and sticking solely to the case in hand... how to correctly install NWN Diamond. If not yet posted to GoG forums, that is a more appropriate residence than here.
My intent is not to fan the flames of discontent but rather, try to form some perspective while targeting the best area to broadcast relevant information like this.
Carry on...