Take a look at Adjusted Net Yards Per Attempt (courtesy of PFR), which with just one number incorporates passing efficiency, interceptions, and sacks. Since the dawn of the modern passing era, passing has become steadily more lucrative. But since 2004, the rate of increase in average ANY/A has accelerated. The 2011 season featured the most successful passing game ever.
For context, compare the graph above with the next one. This shows the same trend but for rushing yards per carry. There is a very shallow increasing trend since a trough in the mid 1990s, but it pales in comparison. The jump in net passing last year alone is larger than the increase in rushing over the entire period. (I've kept the scales of both graphs identical for a pure comparison.)
Looking a little deeper at the stats that comprise ANY/A, we see that they all favor more a successful passing game. Simple raw yards per attempt has steadily increased by a half yard over the past decade. (Note the scale is magnified in this graph.)
The risks associated with passing are declining as well. Sack percentage is declining and becoming less variable from season to season.
Interception rate is also steadily declining.
These trends mean that, yes, the trite notions that today's football is a passing game and the NFL is a quarterback's league are undeniably true. It's been that way since the days of Joe Montana. The more important implication is that the game should be played very differently than conventional wisdom traditionally dictates.
First, offenses should be passing much more often than they do. The league's run pass balance should probably be closer to 15% run 85% pass than the 40/60 split it's been in recent years. It's impossible to know the optimum league-wide ratio until teams start pushing toward the true equilibrium, but basic game theory makes it clear we're far away from the optimum. Of course, game situations dictate a bias toward run or pass in specific games, but overall, the baseline rate should be much more pass heavy.
Second, the more and more successful offenses become at moving the ball, the less important field position becomes and the more important possession becomes. When teams punt, they are making a trade-off. They are purchasing field possession at the cost of some probability of possession. The easier offenses can advance down field, the less important field position becomes and the more valuable possession becomes. Turnovers of any kind become more costly. Sacks become less damaging because it's easier to make up the ground lost. Going for it on 4th down and occasional onside kicks make more sense every year that offense continues to gain a bigger edge.
Teams have yet to truly exploit this shift in the sport. The run pass ratio has barely crept toward more passing over the years. Although the run/pass balance has shifted about two percentage points in the past decade, it's been relatively constant since the mid 1990s. It almost seems like there is a ceiling at 56%.
Run/pass balance should be moving toward passing far faster given the relative strength of each play type.
There are practical considerations that may mitigate a pass-heavy strategy mix. Coaches don't want to expose their high-priced QBs to injury. There are also arm-fatigue and receiver-fatigue considerations. These are real concerns, but they may be exaggerated. Consider our friends from the Great White North who defy these worries. Due in large part to its three-down format, the CFL's run/pass balance in 2011 was 36/64, much more pass-heavy than the NFL, and no one's arm fell off that I'm aware of. Plus, the CFL plays an 18-game schedule, which means more total passes.
There are also strategic arguments for running. Offenses need to run to constrain the defense, keeping linebackers and pass rushers honest, and offenses need to run to set up the play action pass. I have no doubt these arguments are true, but it appears offenses are running far more often than needed to keep defenses on their heels.