Purchased new from Dell, August 2002
It's about the right time frame. You don't see a whole lot of newer boxes, if any, requiring a double set of RAM chips to pass the powering up RAM check.
The reason for the dummy chips is apparently to fool the system into believing that it's got a double set of chips (parity). If you have four RAM slots, you must either fill two or four slots.
If you put one RAM chip or three RAM chips in, the system will puke before it loads the OS.
Thus, your extra dummy chips.