Originally Posted by
Loose Chain
bicycles used to be hand made or at least touched by human hands and as such were never absolutely perfect like computer robot machine stamped out in the box factories modern bicycles.
My experience is that modern, machine built frames are no better aligned than old-school frames with horizontal dropouts. One of the advantages of the vertical dropout is consistent placement of the derailleur pulley with respect to the cogs; this became particularly important with indexed shifting, and I suspect this is the primary reason vertical dropouts have come to dominate on modern frames.