His numbers did not drop once he left Colorado. His career wRC+ is 139, the last 3 years it has been 149, 154, 141. His career wOBA is .396. The last three years it has been .397, .395, .378. His overall line is just as good since he left town.
And has far as his splits are concerned, they are not closer because of his home stats dropping significantly. His road numbers have improved just as much as his home stats dropped.
His last full year in Colorado (2008) his home/road wRC+ was 152/128. His first full year in St. Louis, 154/145. In 2011, he was actually better on the road, at 150/158.
And as for his slugging dropping last year, I think losing a hitter of Pujols' ilk in the lineup, turning 32, and the general ups and downs of baseball are reasons enough for that decline.
So basically, I feel that my point still stands. Good hitters will change their approach upon leaving Colorado, allowing them to produce just as well as they did while with the Rockies.
Further evidence can be found when you look through the past 12 years of park effect data (http://espn.go.com/mlb/stats/parkfactor
). Coors is not the consistent number 1 team in terms of runs, hits, hr, 2b, or 3b. 2012 is the only year where it runs away with most of the categories. The Coors Effect is a very overblown concept imho.