I don't think it's accurate at all to claim that pre-release impressions are always positive because the reviewers want to continue to receive review material from the publisher. For one, if a pre-release impression is negative, it will be in the interest of the publisher to change that opinion by following up with improvements.
What happened in Lair, I believe, is very specific. The reviewers all saw the potential of the game *if* it were closed off properly. The preview levels (e.g., the bridge battle and the sea serpent fight) are impressive in their own right, but they were also work in progress. Most were happy with the experience.
It's unfortunate that Sony went ahead to release the game shortly after. Part of the game is thus left in "pre-release" state. I guess some reviewers were shocked to realize that, and marked it down fiercely.
However, in my view, these reviewers also failed miserably in their writeups. They went all over the place and talk about irrelevant and strange reasons that sometimes even contradict themselves.
The result is a mess.
The game is a 6 in my book at this moment. The control is spot on, but it was not fully debugged in 1 level (The "bombing run" mission). The game will be brilliant if given more testing, polish and fine-tuning. The sense of scale, some of the assets and the very smooth/satisfying dragon flight experience are memorable.
EDIT: This also partly explains why the Lair review scores span so widely... The game is less developed in some ways and yet very "next-gen" in others.