I saw this in a thread on the TF2 forums sometime last year. It's gone now. Too bad, I coulda found the artist :P

Um game reviews officially use a 7-9 scale, where 7 is below average 8 is average 9 is above average. It's sort of like school grades (if your region uses percentile marking). The rest of the scale is reserved for the terrible games and the perfect games. The confusion this causes is why one guy gave Deus Ex a 3/10- this was back when they were deciding whether to use the 7-9 scale or the 1-10 scale, and this guy thought Deus Ex was a bit below average (didn't like the AI and found immersion lacking) so he gave it a 3. With todays scale he would have given it a 7.
movies uses 1-10 where 5 is average.