Essentially, the NCW seat does not have a rectangular footprint which any normal forward facing seat would have.
In order to fit in the same number of longer flat bed club seats as the old cradle seat, it is necessary to increase the number across the cabin from 2-3-2 to 2-4-2.
Obvisouly, in a classic all-forward-facing configuration, the seat would be too narrow. So they decided to increase the shoulder width, decrease the foot width, and pair them up in doubles with one facing forward and one facing aft. The footprint of a pair of NCW seats is rectangular, but the split down the middle between the two is at an angle.
This can be seen more clearly on the seat map at
http://www.seatexpert.com
Hope that helps!
PhilH