YC's MO is to spot value where other VCs don't. When YC started, it invested in young founders. PG is saying that YC now sees female founders in the same light: as marginalized (aka, undervalued), therefore presenting a great investment opportunity.
If the valley's smartest VCs are becoming "Bullish on Women", to use Warren Buffett's phrase [1]), PG's essay is big news for women.
[1] http://money.cnn.com/2013/05/02/leadership/warren-buffett-wo...