Well, that's odd, Snowman. Strangely enough, CoD just seems to maintain the same dpi between the two resolutions, rather than render the same image at a higher dpi with 12x10. Note how the HUD text stays the same, another oddity. I guess different games may handle unique resolution request differently. Maybe CoD accepts custom resolutions by cropping and stretching a standard res, rather than just rendering everything at the custom res? If you can you benchmark CoD, does it show a difference in performance between 12x9 and 12x10? Or maybe CoD just expects fixed-pitch LCDs, not variable-pitch CRTs?
I thought that in 3D geometry is independent of resolution. A circle at 12x9 should still be round at 12x10, just with greater vertical resolution. Apparently that's not the case with CoD.
BTW, it's 4:3, not 3:4. Maybe that's why the picture is weird?

Seriously, can you check if 16x10 is similarly (vertically) stretched?
VIAN, from what I've read most monitor/video card makers just stuck with 12x10 as "standard" for 4:3 CRTs because that res happened to make the most of standard memory sizes. 12x10 fits perfectly into 1.25MB, whereas 12x9 uses ~1.17MB. Apparently programmers went for maximal efficiency over correct geometry in the age of shortening years to two digits (the Y2K problem). Seems reasonable, I guess.