As far as I can tell, the Bosch alternators on the boxer engines with 55 and 65 A peak current were
used this two charging wire configuration towards the starter motor, regardless of the country.
Before the Bosch era Ducellier alternators were used with one charge wire to the starter motor.
Why the charging wires are connected to the starter motor? I think the reason is the manufacturing cost.
Between the starter motor and the battery the supply wires/cables must handle 80-100A safely, during cranking
with approx 400A peak current. This requires relatively long, and thick cable, which is expensive.
By connecting the alternator and the starter motor direct positive together, this precious thick cable will
serve two purpose instead of one, and you can spare a relative long charging wire between the battery terminal
and the alternator (which should be thick also, but not as thick as the starter motor supply's).