You just said it in your post- those buy it, already want it, and their impressions may have an element of purchase-justification. I'm not criticizing gaffers. It's just human nature. I'll find Amiroxs post at some point today, which explains it well.
Either way, they're not worthless- a lot of those impressions are fair/detailed/well thought out. I just don't think they are a representative survey.
Most people that spend their hard earned money on things will give you a much more accurate (detailed critique) representation of it than someone who was just handed said item for free. That usually leads to Narcissistic entitlement behavior which we have seen quite a bit over the years.
It is also human nature to be overly critical of things (Affirmation behavior) when that has been the narrative/rhetoric of the majority of their peers. Why are we have a psychology debate?
Even the highly positive previews from GAF members still point out the negatives of the game. None flat out said it was perfect. I had one of the more positive reviews you will find and even I stated there were things missing from combat and it left way too many questions at the end. Spending $150 and change on the PE does not mean I can not rationally critique the game and point out its flaws.
What I would like to see from RAD in the future
More combat movement options something similar to what snake can do in MGSGZ would be nice the whole laying on your back and firing shots would have worked well in this game.
Better set pieces with more destructibility and more ways to tackle combat situations.
A melee system more along the lines of TLOU which I thought was perfect.
Multiplayer is a given and It would probably be in their best interest to add it in DLC for this game or at least a horde mode to add some replayability while they work on story DLC or the next iteration of the game.
I still think it is a solid effort and hope they improve upon the formula in future DLC or sequels.