Yards are up. Yards per completion are up. Yards per reception are up. Completion percentage is level. Deep passes are slightly down. Sacks are down. Interceptions are down. So how do offenses increase yards per reception without throwing deeper? The answer is Yards After Catch (YAC).
YAC is way up. Last season offenses averaged 115 yards of YAC per game. This season, they're averaging 140. That's an increase of over 20%. In 2010, YAC comprised 50% of all passing yards, and so far in 2011, YAC comprises 57% of all passing yards.
Further, teams are responding to the increased effectiveness of the pass by passing more often. This compounds the effect, resulting in the record setting torrent of total passing yards we've witnessed.
If I had to guess, the underlying cause is the rise of the screen pass. High YAC percentage usually comes from screens and check downs. I don't have data on pass types, but the guys at ESPN do. I bet we're seeing more and more screens, particularly WR screens where one receiver runs a 'pick' pattern. At least, that's what I've noticed with just my two eyeballs.
I've heard many commentators suggest the lockout has somehow had more severe effects on complex pass coverage schemes. I can't rule that out, but it seems like an easy, lazy conjecture--impossible to prove and impossible to reject. If passing were dramatically down this season, the very same commentators would be saying that the lack of off-season practice disproportionately affected complex passing offenses. If field goal percentage were down, they'd say the same thing about kickers and holders, too.