I've seen cynical commenters on HN/proggit/etc. write that the reason why companies like Google are so intent on getting more female programmers, and more programmers in general, is that it'd allow for engineer wages to go down over the next decade or two due to the basic laws of supply/demand.
Not sure I fully buy into it- but it's not a crazy argument either, especially given the recent accusations of collusion to keep salaries low between major tech players.