Just one thought... I've noticed that you said "3 less minutes... and only scored 2 points less". That equates to Fodi scoring 1 point every 3 minutes (or 16 points if he played 48 minutes) while Cerdenia scored 1 point every 2.5 minutes (or 19.2 points for 48 minutes). What others mentioned (defense and such) is probably why the ratings were different. I just wanted to point out that Cerdenia was scoring at a higher rate (although this doesn't explain the discrepancy as well as others already have).
As far as the use of the ratings... on a game by game level I mostly ignore them. In whole I feel they are a good way of getting a feeling for how a players doing and what level (V, IV, III) they could play at and how good their overall game is. My best player doesn't always have the best rating each game but he does have the highest average rating.
No matter where you go, there you are.