MOA means Minute Of Angle. Think of a circle which is divided into 360 degrees, then divide each degree by 60 and you have minutes of angle (and further dividing a MOA by 60 gives you seconds of angle). So 1 MOA is equal to 1/60th of a degree. It just so happens that 1 MOA subtends very close to 1" at 100 yards (it's actually 1.047197580733", but close enough to just call it 1"). The distance the angle subtends is also related proportionally to the range, so 1MOA = 1" @ 100 yards, 2" @ 200 yards, etc.... MOA is useful for measuring groups because it allows a group to be qualified without reference to distance. In other words, if I tell you that my rifle will shoot 1" groups, that really doesn't tell you anything unless I also tell you how far away from the target I was. I could have shot a 1" group at 25 yards, which is 4MOA, which for a CF rifle pretty much sucks. But if I told you my rifle shoots 1 MOA, you don't really need to know the distance to get a good idea of the general accuracy of the rifle.

As for the DPMS you ask about, I don't know if it's worth $2k, but I know you can build your own AR from carefully sourced parts and get it to shoot just as well for a lot less than that.

Mike