A lengthy explanation of the StarCraft II ladder, where it currently stands, and where it's expected to go has been posted.
Adjust league distribution
As mentioned, we’ve identified that the current league distribution percentages aren’t in line with our target percentages. The upcoming distribution changes should allow many more players to be in the correct league, and for each league to have the correct percentage of players based on the figures we announced for Heart of the Swarm. Once this adjustment is made, some players will see a change in their current league placement.
For the full post, click here.
Battle.net - StarCraft II Ladder Update: March 2, 2015