Exactly. Unfortunately no reviewer is an island. His work stands for the entire site, and will be compared to the sites previous reviews with similar games. Hence why the reviewer should have considered the scores for other similar fps his site/colleagues reviewed as you said. That's the whole point of reviews really, so you can access them to other products/games you might rather spend your money on.
A laymen looking at IGN's review scores, would see Turning Point and SoF rated higher than Haze, and possibly purchase the said games over Haze because of it. And I don't think anyone can honestly say they think the other two games are better than Haze. I personally feel Payback is bordering on unplayable purely because the frame rate from the moment the game starts is so damn inconsistent.
There needs to be some sort of guidline set by sites imo, and research on the part of the reviewer should be mandatory. They should not let politics get in the way of review scores. So what if Free Radical has a better track record and you expect more from them, or because they spouted too much PR BS, or whatever other reason, you should judge the game based purely on the merits of the quality of the game itself and nothing else. Using your sites past reviews of similar games as a benchmark. Unfortunately with IGN's reviews, 5 is not the average. It's usually around 6+. But in the case of Haze, Jeff used the entire scale, and as such, it does not line up with the rest of IGN's similar genre reviews.