I'll admit I chose the 300D when I first bought a DSLR because it was the least expensive and had good reviews on dpreview and other sites. With that said, given that there are essentially no DSLRs that get less than "Recommended," to the beginner (that doesn't currently own lenses for their film SLR) the least expensive is most advantaged. At first one tends to think that the "whole system" thing doesn't really matter too much since one does not exactly anticipate spending money on all the expensive lenses. I once thought it was quite an expense to have to spend a few hundred dollars for a consumer grade telephoto zoom. Anyway, little did I know at the time that I would later spend thousands of dollars on lenses and accessories. I wasn't expecting to buy more than the kit lens when I go the 300D, so I never really looked at the "whole system" when I purchased the camera. And then a while later I got my first part-time job, my DPI grew, and I started reading the forums... But that's another story.
So I guess my point is, most people starting out in DSLR photography probably don't consider the fact that Canon has an 85mm f/1.2 compared to Nikon's f/1.4, that Canon has more IS and USM lenses, or that Nikon has a 200mm f/2 VR and Defocus Control lenses.