My Blood-Horse colleague David Schmitz posted an interesting look at the 2009 Kentucky Derby Presented by Yum! Brands (gr. I): Kentucky Derby by the Numbers: Dosage Dilemma. He includes a nice summation of the Dosage calculation and what it represents -- and pedigree watchers will note that Derby winners rarely stray from the "rule" of low Dosage Index and Center of Distribution numbers.
That being said ... the Thoroughbred population in North America these days is being bred largely for speed orientation, so it's natural to assume that over time the average or baseline Dosage Profile will shift to higher ("speed") numbers for all Thoroughbreds, including Derby contestants. It's likely that more and more Derby winners in the future will be true sprinters that can hold out the extra two to four furlongs to complete the Derby distance -- so we'll see that 4.00 DI and 1.25 CD "rule" change accordingly.
Any guesses on what the Derby Dosage rule will be in, say, 25 years?