I think inns should be handled like a must for the game out of all the different aspects of the game:
First off, just think of the crafters who dedicated themself to professions like cooking or brewing. If a smith may have his workshop for crafting and trading, then the cooks and brewers also need a spot for that. Also, those crafted consumables may play an important role, so many people may look for an inn to supply themself up between their adventures.
Also, the RPG-part playes a great role. Yeah, CF is a game of sieging and warfare, but also an rpg where people want to play their c