Oh, I see, I didn't realize the cartridge had a whole other processor in it.
Found this, "DPC+ is an extension of the original DPC chip that was developed by Activision and included in the Pitfall 2 game released in 1982. It basically allows you to update graphics faster and much easier, and also includes more ROM, RAM and better sound. The DPC is actually implemented using a 70mhz ARM processor, so in addition to its features, it also allows you to write game logic in C which is then executed by the ARM. All interaction with the TIA still needs to be done in 6502 assembler."
So it's really like a whole new system given the additional ARM CPU. Sort of.