The comparison photos below compare MechMan units to other manufacturers' high output offerings.  It doesn't take any special training to see the major difference in construction.  Alternators are subjected to MASSIVE amounts of heat, strain and vibration. 

The heavier duty your alternator internal components are, and the larger the alternator is, the better it will be able to dissipate heat.  Furthermore, the more amperage the alternator produces, the larger the conductors need to be in order to physically transfer current without measurable loss.