I don't think the main problem is companies not valuing women, because it starts much earlier. University CS departments are tilted very heavily towards men (~1

I don't think the main problem is companies not valuing women, because it starts much earlier. University CS departments are tilted very heavily towards men (~10:1 at my school) so there are far, far fewer women graduating with CS degrees and entering the marketplace. If many companies have a similar ratio, it may reflect the availability of female programmers rather than any bias on their part.