I might ascribe the discrepancy to both a) assessing games using the 'for what it is' lens and b) defining 'for what it is' by what they've been exposed to. You can quite easily understand the difference between them by trying to understand what games they've been exposed to. If you've never played PS:T, then your definition of what decent video game writing is differs from most Codexers'.
And I think it is the case that games have only recently turned into mass media. Before, a few hundred or a few thousand (those, maybe, that you mention in your post) would ever hear of, much less play, a particular game. Now, millions play mainstream games (and I don't mean mainstream pejoratively, just as a matter of fact) and only a fraction of them have been exposed to other, perhaps better, games--the dissenting, cranky few who enjoy pissing on Bethesda and Bioware. This lack of exposure may be age related, or just the age of particular interest in video games, or perhaps class related (let's not kid ourselves--almost anybody who played Fallout when it was released was upper-middle class in a handful of ultra rich countries, so yes, this is a class issue).
One reason this gap continues to exist is the way games age--or rather the way they don't. I happen to be one of those people who enjoys getting old games to run in emulators on a fucking awful OS. But Jesus if it doesn't kill half the energy and time I had for the game I'm trying to run in the first place. Also, I suspect that it isn't in the best interest of video games as an industry to do anything but dismiss the old and hype the new, regardless of quality.
An auxiliary observation, to deal with the natural counter example, i.e. those gamers or game critics weaned on Oblivion and the likes who go back and play 'classics' but still prefer the former, is simply the appeal of the new. How many times can you become completely immersed in a world? Maybe as many as there are radically different and well presented worlds, but the fact is that we criticise Bethesda and BW for turning into derivative, uncreative drivel. But for somebody going the opposite direction, the excellent games, the titans of a particular genre, are just variants on something they already know. It's not new. They can't get really immersed in a world they've already visited, even if it's better, because it already smacks of the old and the semi-familiar-but-off.
To answer more directly your question, I don't think either are idiots. The Codex is classist, elitist, uncompromising, self-entitled and ridiculously hyperbolic. The 'mainstream' lacks a real critical approach to games, is a tool of games as industry, and can't see past the end of its nose. But they both are operating by the same logic as they react to and criticise games.
EDIT: Ninja'd, but I'll leave it because I think it expands on the above two posts.