When you are a top player like the williams and the belgians you want it all. GS, titles and the no.1. Anything less is unacceptable for them. To be at the top you need all three.
Personally i feel that although Venus already had 4 GS, tonnes of titles and weeks at no.1, she is still underachieving. She should have won more GS and had more weeks at no.1.
Serena seems to be living up to her full potential.
Justine and Kim have only started and are seriously raking n the titles. The ranking (for Justine) and Gs (for Kim) are gonna fall into place.