Why Don't the Women play 5 sets in Grand Slam Tennis?

I'm just sat watching the tennis. The French Open, Women's Singles Final for 2015 and, as usual, I am wondering why the women get away with only playing 'Best of 3 Sets'. The Men's Final is 'Best of 5 Sets' so why the inequality? Surely, in times where equality is pushed with such fervour (rightly so), it is only right that the women get the same prize money for the same level of achievement. I also wonder which female players would benefit most from having to play similar length matches to the men. Would the same players be in the Top10 or are there better athletes waiting to show their staying power over a greater match time? When are we going to see this inequality addressed and which will be the first of the Grand Slam tournaments to level the playing field? My money is on the Australian Open. Equal pay for equal roles. #OnlyFair