There can be several factors that make newer pickups sound different than older ones. One is the how the magnets were cast and the dimensions used for a particular pickup. The quality or even lack of quality added to the total performance of the pickups. The way the coil was wound such as hand winding commonly know as scatter winding where the magnet wire is placed on the bobbin in a random manor.

Machine winding is more commonly used today for larger and faster production runs where less labor is required. Modern coil machines can wind up to six bobbins at a time, which really reduces production time. I feel machine winding takes away much of the character especially in vintage restorations or rewinds. Much of the sound comes from the layering and winding tension which affects the tone of a pickup.

Newer pickups use magnets made from Alnico or Ceramics which can be made to closer tolerances in given specifications. The insulations today have a different chemical composition as compared to the material used in the late 40s and 50s. The layering of magnet wire to a desired number of turns per layer can change the inductance and capacitance and the tolerances on the volume and tone controls. The newer manufactured volume and tone potentiometers can have closer tolerances as compared to the earlier ones used.