The Lord of the Rings: Return to Moria is rated 'Fair' after being reviewed by 7 critics, with an overall average score of 66. It's ranked in the bottom 30% of games and recommended by 14%...
Think of it this way : should games that people pay money for be below average, ie, failures?
Anything below 60% shouldn't even see the light of day, really.
Seen like this, it seems a lot more reasonable to me that 30% of released games would be below 70%. In fact, I'd say it's still way too many games that probably should still be in the oven.