FAQ says:
How do the dice work?
The dice are based on high quality random numbers from Random.org. The numbers are read from a large file containing columns of numbers from 1 to 6, in the format A1 A2 A3 D1 D2. When the dice are rolled, the game engine reads a line from the file and discards it. The appropriate numbers are used and the others are ignored. The file contains 500,000 lines of dice rolls and is re-loaded when all the lines are used up. As of November 2006 we consume 125,000 lines of dice rolls per day.
The number of different dice combinations is 7776 (6*6*6*6*6) and 500,000/7776 is slightly over 64 (64.3004). If every combination was represented the same number of times then there would only be 497,664 lines of dice combinations.
Question 1:
How have the remaining 2336 lines of dice combinations been determined?
Question 2, and more importantly:
With all possible outcomes not all equally represented, are the dice truly random?