OP:

Do you mean sealed "CARTRIDGE" bearings? The kind you finger torque down, then fix with another nut and voila... it's smooth as silk, a bit stiff maybe due to viscosity and seals touching, but super silky smooth?

The main reason few manufactures make this is cost. You need precise CNC machines that start with precision molded and cast parts. Gotta have tight tolerances to allow for a smooth press fit without any play, but not be too tight as to cause the bearing cartridges to bind. With cup/cone hubs, BBs, etc., there is more tolerance for spacing, and imperfections in metal surfaces. Just try out a new Shimano Deore or Tiagra hub. Feels rough, not silky smooth. Ride on that hub for about a week, and then feel it. Smoother. The bearings will wear a small groove in the cups and cones and flatten small (i.e. tiny) imperfections. And most of this is inconsequential to overall friction, which the sealed cartridge bearing unit probably has more of, because it's internal grease and seals exert more friction overall.