I'd say you're having trouble because most of those tunes are really difficult to categorize into a genre. Most RPG town themes never fall into one category of music.
Most commonly though, it's just a more relaxing piece of music that is either a lullaby or ambient tune.
Like, in most of the examples so far, it is basically a string instrument (or something emulating one) playing a progression of arpeggios and a melody. Wind instruments, a music box or another string instrument usually carries the melody. There is usually not much in the way of percussion either. It's all pretty minimalist. As for harmony, just use a lot of extended chords etc. in either a major or minor key. Lots of 7ths, 9ths and Sus chords for example.