D-Activator has great harmonics like the Norton, but it is very crisp, clear, and "precise" if that makes sense. Much higher output. It won't forgive sloppy playing. If you have a highly refined picking technique, and you want crisp, high output, then you will love the D-Activator.
Norton is more laid back, much warmer sounding, higher harmonic to output ratio. If you want something warmer and a little older-school without being too old school, and you like to get nasty and squealy, then you will love the Norton.
Norton is a very dynamic pickup, but the D-Activator may be the one pickup in Dimarzio's stable that is even more dynamic. That is where the primary similarities lie.