Fudo,
Good observation. There are a couple of major differences that come into play.
First, blade thickness. The Mk2[Marine Combat Knife] is .167" blade stock. The BK&T C/U-7 is .188". The BK&T is also a much wider blade, with the Mk2 being approx 1.25" wide, and the C/U-7 being 1.61"[not including the thumb ramp].
Secondly, the fuller, or blood groove, limits how high you can grind the primary bevel on the blade. On the Mk2, the primary bevel is only approx. .6" long, whereas on the C/U-7, its approx.1.32" long! This leaves a section of unground, full thickness stock approx .3" wide, for additional strenght.
These differences, coupled with the full width tang, make the C/U-7 a MUCH stronger knife....esicially with regard to lateral strenght. Also, with the "higher grind" is is a much better cutter. And it only weighs 2 oz.s more that the Mk2 Combat Knife!