Congratulations -- you are one of the top new Drupal Answers - Stack Exchange users for the week of Apr 18 2011!
The link seems correct to me. It links to the league page of the week containing April 18.
On SE sites, the weeks are considered starting from Sunday, and ending on Saturday.
Sorry, this was a bug on our end and has been fixed.
We also clarified in the email, if you have < 200 rep, that only >= 200 rep users are tracked in the network-wide leagues.