Everyday systems have one monitor and one video card.
Multimonitor systems just extended that capability to allow users with two video cards and two monitors have twice the desktop space, bonded together through Windows's software. While Matrox wasn't the first to introduce a multi-monitor card, they were certainly the first to bring it down to the levels of everyday consumers. Lots of folks out there have an extra monitor laying around, usually an older screen they tossed in the closet after they upgraded to bigger and better. Now, this may seem like a very small crowd who has this problem, but think of this. Thus, eDualHead was born.