Security tends to feature more prominently: physical, financial, psychological and emotional.
First, the physical: so many Harlequin men are tall, dark, handsome, and muscular because that means they are physically imposing. They can protect Heroine from harm and beat up bad guys and Heroine has to lean up to kiss him.
Financially, when was the last time anyone read about a poor Duke? Even if Hero is a manual laborer, he'll be at least comfortable. That's because living happily ever after in a dingy one-bedroom third-floor walk-up is not anyone's idea of romance.
Psychological security is one of the hardest to define, since it has a lot of overlap with emotional. One of the biggest ways psychological security is woven into romance is in that Heroine will not be awkwardly more intelligent than Hero, and if she is, he'll think it's sexy, not be threatened. Heroine is free and safe to be exactly who she wishes to be.
Emotional security is the one at the heart of romance: by The End, both Hero and Heroine must know that the other loves them completely. The love must be mutual, providing security that Heroine nor Hero will not have their heart broken later. In true Western fashion, the love will also be monogamous, and promise to last lifetimes.