Interesting read. I have a certain bias against statistics, though. They only tell us trends, or as the link states, a "baseline of the whole league." The actual truth is in the details. It's one thing to say a pass is on average a better call, but what if you have Emmitt and the '90's o line and JaMarcus Russell at QB? I'm betting on the run.
Or as the link says, "Play calling is never as simple as just run or pass, and there are many different types of passes, ranging from deep bombs to short screens. Additionally, there is some amount of bias in the data. Teams that are good in passing would be expected to pass more often, and teams good in running would be expected to run more often. In other words, we can't just tell the 2009 Browns to pass far more often on first down because their particular expected payoff for passing may not be any better than for running."