Like the others I don't believe it's a requirement but I would certainly mention it to my clients. Some cultures in fact consider a vent to the exterior a must because of the types of food they typically cook. For example I do a good number of inspections for Indian clients, my community has a large Indian population, and without exception they want that done right away because of the spices used in cooking.

But I wouldn't call it out as something that SHOULD be done but rather an option your client might be interested in.

__________________
Principles don't change with circumstances. That's what makes them principles.
-George Colombo