I wouldn't call it far-fetched.

It's not just two adults, it's still between a father and son. Although corporal punishment is commonly linked with children, it can still happen between adults.

Also, does that change really impact anything?

A good look into this can be found here and here.
Basically, corporeal punishment is something that is controversial in the U.S. A possible reason why this was changed was to avoid having Ryoma seem like an abusive father.