The problem is that the 77 cents figure tells us nothing, and leads to useless solutions. It is technically correct, but that isn't really the best kind of correct. Just a few of the causes of the gap are the fact that women make up a tiny percentage of the applicants for the lucrative building trades (among the highest paying blue-collar work), the fact that far too many women take largely useless majors such as Communications or Sociology (interesting, but useless for seeking employment) instead of engineering or accounting (where the money is), or the simple fact that most of the country's income goes to a fairly small group at the top in which women are underrepresented.
NONE of these can be addressed by the most popular proposed solutions (laws preventing unequal pay won't help when the pay gap is between professions rather than individuals within that profession, laws mandating X percentage of new hires be women won't help if women make up less than X percentage of applicants, etc), and the only solid solution (a concerted attempt to push the notion that building things and figuring out how they work is just as much for girls as being a nurse or teacher, particularly in media aimed at children) to the first two will take years to take effect even though it has already been implemented at least on a limited scale.
Now, there's avenues to reduce the areas of real discrimination - requiring employers to post the wages of every employee in the break room, for example, would go a long way. These just won't make that much of a dent in the 77 cents figure.