Together with Venus is also interesting Ana Ivanovic case which is between 2005-2007 always TOP5 (if not TOP3) in aces and aces per match, but this season is "nowhere" in that category. This season she not only switch her racquet (from Wilson to Yonex), Ana also completly change her serve strategy, so her fastest serves now is about 180km/h, not almost 200 like in past, and number of aces is totaly down. But on other hand her "1st serve in" percentage grow from 50-55 to 60-65 and her average speed of 2nd serve is faster now so its hard to say that her serve is "worse" now.
Good example is comparing her serve stats from Roland Garros 2007 and 2008 where she in both cases played her season best tennis reaching finals. In 2007 Ana finished RG with most (36) aces than anybody and her fastest serve is 201km/h, but this season she finished with 20 aces and 190 km/h fastest serve - but on other hand last season she at only three (out of 7) RG matches finished with higher 1st serve percentage than 52% and this season only once her "1st serve in" percentage is under 55%!
and I'm not even fan of Ana Ivanovic... just an objective observer who realize how perfect she is
AMAZING BELGRADE MIRACLE: In just three years (2008-2011) 5 different players born in same city reach world #1 in rankings and several GS titles and finals (WTA singles: Ana Ivanovic and Jelena Jankovic, ATP singles: Novak Djokovic, ATP doubles: Nenad Zimonjic and Daniel Nestor... with notable performances of Bojana Jovanovski, Janko Tipsarevic and Viktor Troicki which is also all three born in Belgrade)