Think again. This interesting article by Slate explains how women consistently serve at speeds comparable to their male counterparts.
Sabine Lisicki (picture above), broke Venus Williams record for fastest female serve this past summer at the Bank of the West Classic, clocking in at 131 mph. That serve was faster than any serve Roger Federer produced during 2014. It's barely slower than world #1 Novak Djokovic best serve this year and "equal to or better than the fastest serves of at least 29 men, including" many seeded players.