Those CPLDs are doing all the address decoding for the ROM chips for the various games. It would be interesting to know if they've set the security bit in the programming; if not you could find the JTAG connector on the PCB and read the contents out again. In theory with the CPLD's you could use ROM chips with different faults on different boards to lock out different regions - but you would require a unique CPLD program for each PCB. I suspect they try to place chips with the same fault in the same position on every PCB to minimise the different CPLD configurations required. Those shorted pins look like they're next to the power pins on those devices.
I'm curious about the origin of the "Dick Smith Invaders" game. You say it was programmed by contractors for Dick Smith, but it is clearly a port of "Tandy Invaders". Or vice-versa. Any further info on that?