Factual error: The film is set in 1951 but Peter and Adele have their first dance to the tune "Stranger On The Shore" which was first released in 1961.
Factual error: In the very end, when Peter is returning to town, as the train rounds the bend you can see much newer style electrical transformers on the power poles. If you look close you can see a modern style street lamp also.
Factual error: The locomotive used to haul the train that takes Mr. Appleton back to Liberty after facing judgement is an Alco Century series - which weren't around in 1951. Nowadays, the locomotive type is actually semi-vintage, but it is obvious that this particular one has been patched up and modified over the years. It has intercoolers, ditch- lights above the pilot and a blank nose where the lower set of headlights used to be. In 1951, the locomotive would have been a steamer, or an early EMD F3 or Alco PA Diesel streamliner.
Factual error: If you look carefully you will see that all the cars have license plates with 7 characters on the plates. California did not introduce license plates with 7 characters until the early 1980's.
Answer: Two possible reasons. 1. Hitting him back and telling everybody about Bob being a complete jerk would make him no better then Bob. 2. Bob actually knew the real Luke and if Peter had hit him, Bob could retaliate by telling everybody the truth.