I know that Edge grades on a wider scale in general. I also haven't played the game, so I can't really offer any judgment. However, I will say this:
A game being polished is different from a game simply not having glaring or game-breaking bugs. The number of really polished video games we get every year is actually very small, and I do think that a highly polished game (say one that offers a smoother experience than 99% of the other games released every year) should indeed get above a mediocre or average score, whether or not the reviewer agrees with the design philosophies of the game. You don't give Starcraft a mediocre review just because you've never liked an RTS -- you grade it mainly based on its execution.
Second, it seems to me JRPGs are getting the stuffing beaten out of them by reviewers this generation. Again, I don't know whether FFXIII is an incredibly polished game (it may just be the graphics) but reviewing something based on the direction you think games should go in or based on the type of games you prefer and want to see more of is not something that video game reviews have done very much in the past. If it becomes more standard to do so, reviews may behave very differently in the future. For example, if I were to honestly review first person shooters on consoles, based on the amount of enjoyment I get out of them, most would average around a four or five, with a few going up as high as seven.
Again, I'm not saying that's what's going on with FFXIII, but if it is a very polished and well-executed game I think there will be a pretty clear trend of extremely polished JRPGs getting review scores that rank them next to cheap movie game tie-ins and shovelware, and if that's the case, the fanbase for JRPGs needs to start making some (fucking) noise, because the last thing a genre that very few are bothering to invest in needs is a bunch of professionals telling consumers to stay away, with no other clear voice telling them those reviewers don't know what they're talking about.
