a town this small shouldn't have any kind of restrictions requiring a deck. The only likely issue is if there is some kind of dangerous drop off due to lack of porch/deck from the doorway. The deck would be in most cases an optional item not a requirement. In very restrictive neighborhoods it may be a requirement to have a deck but not likely in Hudson indiana. Your inspection should have addressed this lack of deck if there is an issue.
Interesting question and like most of the other answers I am curious has to why it was illegal for your agent to sell you the house without a deck? A deck is typically an "optional' item. Did you have an inspection? Was it pointed out during the inspection that there was an issue with the fact that there was no deck?
I agree that it sounds odd to be illegal to sell a house without a deck, but if you feel there is an issue, I would contact the agent's managing broker as a first step. The broker will be in a better position to help resolve a dispute such as this.