Toward a mechanism for infidelity

There were two intriguing UCLA studies on women reported earlier this month:

One study published today by the University of California, Los Angeles Center on Behavior, Culture, and Evolution and the University of New Mexico says women have evolved to cheat on their mates during the most fertile part of their cycle, but only when those mates are less sexually attractive than other men...
A related study, which will be published in Evolution and Human Behavior, finds that women are more likely to fantasize about men other than their mates, but only when they don't consider their mates to be particularly sexy.

There was also this bit of research on men which came out earlier this month as well:

Research published in the recent issue of Ethology has discovered that men are able to potentially use smell as a mechanism to establish when their current or prospective sexual partners are at their most fertile.
Axillary odour from women in the follicular phase was rated as the most attractive and least intense. On the other hand, highest intensity and lowest attractiveness was found during the time of menstrual bleeding.
The results suggest that body odour can be used by men as a cue to the fertile period in current or prospective sexual partners. Therefore, the fertile period in humans should be considered non-advertised, rather than concealed.

The logical inference is that men can detect when women are most likely to stray and act upon it. Sexually attractive men would stand to benefit most from this.