Re: 2011 Schedule & Ranking
Here's the rule to explain the "committed":
In 2011, any player who finished in the 2010 year-end Top 30 will be required to compete in four Grand Slam tournaments and eight ATP World Tour Masters 1000 tournaments. In addition, the Best 4 ATP World Tour 500 and Best 2 other events (ATP World Tour 250 and Challengers) will be counted towards a player's ranking. All direct acceptance players at the time of the entry deadline who do not play will receive a 0-pointer in their ranking.
So Top 30 are committed by ATP to play certain tournaments and got penalized if they don't.