Apparently, it's a weak but full field set to race for a Win, Place, Show slot...
http://www.dispatch.com/live/content/sports/stories/2010/04/27/ready-or-not-horses-fill-up-derbys-field.html?sid=101snip
As the sport's overall popularity has declined, the Triple Crown races are the only ones that continue to appeal to a broad segment of the public. Every rich owner who gets into the game now has the same aim: to win the Kentucky Derby. Trainers know, too, that the way to make their reputation and attract more clients is to win the 3-year-old classics.
Another factor has undoubtedly affected the thinking of owners and trainers this year: the memory of Mine that Bird. The gelding's Derby victory in 2009 was one of the most inexplicable upsets in the history of American horse racing. Mine that Bird gives hope to every owner and trainer with an underachieving 3-year-old. If it were not for the 20-horse rule, this year's Derby might have had as many as 30 entrants.
Yet the reasons for caution about running in the Derby are the same as they were in Whittingham's era. No race in America is so stressful. Three-year-olds are being asked to run farther than they have ever run, against the largest field they will ever see, under conditions that invariably produce bumping, jostling - or worse. The race always takes a toll on its contestants.
Last year, after one entrant was scratched, a total of 19 horses started in the Derby. Of them, 16 did not win a race for the remainder of the year. Six didn't race more than once. Promising colts regressed and couldn't regain their form after their Derby venture. It is understandable that almost any owner or trainer wants to experience the excitement of the Kentucky Derby, but it is an experience that often comes at a high price.