Geometry, the cockpit is shorter on womens bike and the top tube is possibly lower, it would also feel more cramped to you but more comfortable to your wife (in theory, some women like the non women designs better), the only way to know if your wife will like the men or women design better is by letting her ride the bike, I know of quite a few women who like men designs better and its not like they are burly women or anything lol.

Oh and the Hardrocks are awesome, definitely my bike of choice under 400$.