I think some other games have this problem. Do you know if the authors really submitted their code?
I think I can actually shed some light on that for this year. In the game submission, you have the option to show the source code after the competition is finished. If you select this option, it shows the "show source code" link on the main page, but it doesn't show the code.
I can't speak for the earlier years, but I believe that all the code will be available to look at after the voting process is finished.