Perhaps that statement would be only true applied to Europe. As the culture that produced Wall Street fraud, Robber Barons and Wild West Capitalism, the American upper classes are rarely concerned with codes or norms. In general, the rich in the US are beholden to few expectations of conventional behaviour except those that they make themselves. That's why Tom and Daisy Buchanan, the rich, unhappy, and unhappily married couple, still manage to ride off scott free into the glorious sunset in The Great Gatsby as the ultimate winners of the game that Jay Gatsby played but didn't understand.
The best thing that can be said about Trespass is Joel Schumacher recognises why Funny Games didn't work at all as an American film and constructs a more plausible scenario where the comfortably rich yet unhappy family toss all sense of decorum into the wind and audaciously turn the table on their hapless captors using their upper middle class wiles and cultural capital. The result is a thriller stuffed with very implausible yet entertaining twists and reversals.
Very suitably, Nicolas Cage is cast as a diamond broker who attempts to out-talk, out-wit, and out-scream his hapless captors, at several points holding both the literal and metaphorical gun to their heads instead. Nicole Kidman plays the unhappy stay-at-home architect wife who may or may not have had a fling with one of their captors, who are after their diamonds and riches, failing which they'd just take a kidney or two, thank you very much. Ben Mendelsohn plays the criminal mastermind whose plans start to unravel because his upper middle class captives aren't Europeans but brash Americans.
Trespass has all the ingredients for a trashy B-grade thriller and wouldn't disappoint if that's what you're after.