The difference is that Vika displayed stroger results at majors (winning two back to back and being a finalist elsewhere) than Kvitova, who had largely been an inconsistent washout at every major other than those spaced-apart Wimbledon titles. For those who like to count runner-up or late stage finishes as part of the player file (I am content to just use the majors titles), then between the two, who has been more of a tour force at the majors?
Kvitova's highest level at the majors:
AO -SF 2012
FO- SF 2012
W- WINNER 2011, 2014
USO- QF 2015
Vika's highest level at the majors:
AO - WINNER 2012, 2013
FO - SF 2013
W - SF 2011, 2012
USO - FINALIST 2012, 2013
Even if we use my standard--majors victories only--they are tied, but Vika was strong enough to defend her title. Kvitova simply did not have that kind of consistent game.
Kvitova needs more than Serena to fade before she can pile up majors. Should she avoid Pennetta? How about Sharapova, who beat her at the AO and FO?