In addition to the points above, it is important to note that both stories discuss specifically what it feels like for a woman to be trapped in a marriage. While Minnie Wright from Trifles is much more proactive in escaping her "trap," Chopin makes it quite clear in "Story" that Louise Mallard has felt trapped for many years in her marriage but was either unwilling or unable to take action to escape.
Similarly, both works portray a natural tension between the sexes. In Trifles, the men trivialize Mrs. Hale's and Mrs. Peters' comments and abilities which causes them to completely underestimate them. John Wright minimized his wife's needs and desires and probably never suspected that she would be strong enough to present any danger to him. In "The Story of an Hour," everyone pities and caters to Louise Mallard after her husband's death, assuming that she is devastated by the loss of her provider and protector when in reality she is overcome with joy at the thought.
The theme of the stories gears toward the oppression of women by marriage. The women are basically victims of the place in which society expects them to be as far as marital and family roles. They are stories about the the expectations that society has bestowed upon women and how many times those roles are simply not in tandem with what women really want or need. The theme also gears towards the mercy (and lack thereof) of which these women depend in order to be considered "ok", or "normal", and even to be forgiven by society. Ultimately, the theme is one which exposes the sad reality of oppression and gender discrimination that is unique to specific times in our history.