Note that I used, "These simple RAM cards just top up motherboard RAM", with the key word being "simple".
By "simple", I'm speaking of RAM cards where all the support chips do is basically address decoding.
More advanced cards will have their own pool of RAM which can be used for various purposes (RAM top up, expanded memory, print spooler, etc.)
That requires extra circuitry.
The MEMO576 is a "simple" RAM card, and when I look at the Quadram Short RAM card, I see an almost identical card.
At
http://members.dodo.com.au/~slappanel555/manuals.htm