This isn't difficult to believe since most sex selection is probably attempted by couples. Most guys still want a son.
If you look at overseas adoption, however, you will find a number of single mothers adopting girls. If it ever got to the point that large numbers of single women could choose to have say....one child, I'd be willing to bet that most would want girls.
Not arguing with any of your points, but in a lot of overseas adoptions - particularly in China - it is mostly baby girls that are available.