I do not believe this is true Film Noir. Just because it is about "gangsters" and black and white, and happens at night does not make it Noir. It has none of the artistic shadow & light styling. Not Femme Fatale (Yes a strong female lead but not "Fatale") and no doomed hero.
They made "common" movies in the 30s and 40's too. Black and white film, fedora's and night does not make film noir.
I agree with you completely and so does the ghost of Jack Narz.
Let it be unsaid: insignificance is the locus of true increpation.
Your evidence for why this film is not film noir proves rather empty when one considers the following article on Film Noir from Wikipedia:
The questions of what defines film noir and what sort of category it is provoke continuing debate. "We'd be oversimplifying things in calling film noir oneiric, strange, erotic, ambivalent, and cruel": this set of attributes constitutes the first of many attempts to define film noir made by French critics Raymond Borde and Etienne Chaumeton in their 1955 book Panorama du film noir américain 1941–1953 (A Panorama of American Film Noir), the original and seminal extended treatment of the subject. They emphasize that not every film noir embodies all five attributes in equal measure—one might be more dreamlike; another, particularly brutal. The authors' caveats and repeated efforts at alternative definition have been echoed in subsequent scholarship: in the more than five decades since, there have been innumerable further attempts at definition, yet in the words of cinema historian Mark Bould, film noir remains an "elusive phenomenon ... always just out of reach".
Though film noir is often identified with a visual style, unconventional within a Hollywood context, that emphasizes low-key lighting and unbalanced compositions, films commonly identified as noir evidence a variety of visual approaches, including ones that fit comfortably within the Hollywood mainstream. Film noirs similarly embrace a variety of genres, from the gangster film to the police procedural to the gothic romance to the social problem picture—any example of which from the 1940s and 1950s, now seen as noir's classic era, was likely to be described as a "melodrama" at the time. While many critics refer to film noir as a genre itself, others argue that it can be no such thing. While noir is often associated with an urban setting, many classic noirs take place in small towns, suburbia, rural areas, or on the open road; so setting cannot be its genre determinant, as with the Western. Similarly, while the private eye and the femme fatale are character types conventionally identified with noir, the majority of film noirs feature neither; so there is no character basis for genre designation as with the gangster film.
The final scene, as Kay and Frankie walk into the fog, is certainly a fine example of noir imagery.