I was searching along for some answers and found this:

http://www.left4dead411.com/left-4-d...rsus-preview-1
EDIT: Its the same link you posted actually... haha

The scoring system is a little complicated at first. After the Survivors reach the safe room or the Infected kill off them off, a score is given to the Survivors. The score calculates the average distance traveled by the Survivors (total of the distance traveled by each Survivor as a percentage, divided by 4) and adds this to how much real health they have at the end (after applying held health kits, pills don't count since they're only temporary health). This number is then multiplied by the number of Survivors alive. This is multiplied again by a difficulty modifier given to each portion of the map. These seem to be anywhere from x1 to x2. In a full game, each team will finish with five different scores, which are then totaled together. The team with the most points wins.

{(Average Distance Traveled) + (Health Score)} * (Number of Survivors in Safe Room) * (Map Modifier)