@snood,
It seems like over the last decade, the way to show you are worthy of the number one title is to compete with Serena. Capriati, Henin, the young Sharapova, Clisters can all say they had a time where they could go head to head with Williams and have a chance of walking off with the hardware. Azarenka has had a great season, won four titles including the Australian Open and put together a great first half of the season (this is only her third loss in 2012) but the story for both her and the resurgent Sharapova is unless you can compete with Williams, there will be an asterisk by your name when people talk about your number one ranking.