Hi Dick
your observation is correct.
The RC winches are using a standard container where the attachment wedge allow for a vertical fixation of the"box". Naturally is much easier to fix a support plate horizontal inside a hull during construction and much easier to have access to the winch fixation bolts, hence the drum being also horizontal.
To overcome the possible fall out of the string it is generally used a close loop string with an elastic to keep the tension. Myself I mount one of the pulleys with an elastic/spring. In 20 years I never got any fall out of strings ! probably lucky !
The vertical drum has less access possibility once inside the hull.
Further you can also adds eyelet guides very close to the throat of the drum as depicted in your picture.
Cheers
ClaudioD