When did it become "a pass-happy league"?

Take a look:

YR #teams>4000 yds passing #Teams>2000 yds rushing

1997: 0 (0)---------------------------- 6
1998: 3 (2)---------------------------- 8
1999: 4 (5)---------------------------- 9
2000: 5 (3)---------------------------- 11
2001: 1 (2)---------------------------- 6
2002: 4 (4)---------------------------- 10
2003: 1 (2)---------------------------- 11
2004: 5 (5)---------------------------- 9
2005: 4 (4)---------------------------- 9
2006: 3 (5)---------------------------- 9
2007: 7 (7)---------------------------- 7
2008: 5 (6)---------------------------- 9
2009: 12 (10)--------------------------- 10

(In parentheses are the # of QBs that total >4000yds. The differences between the team and QB totals I think may be due to database squirreliness or maybe team yds and individual yds are accounted for differently.)

A few other interesting facts:

The average team rush totals have been nearly constant over this time period (2009-1867 yds, 1997-1808 yds).
The average team pass totals have risen roughly 10%. How can this be? Remember there was a rule change at one point that reduced the time between plays, so today's game has more total plays made.

The most telling stat but sometimes overlooked:

In the late '90s the good QBs had typical completion %s of about 60%.
In mid to late '00s the good QBs had typical completion %s of about 63-65% (and Brees this season had an incredible 70.6% completion rate). So either the talent level of the QB has greatly improved, or the rules have made it easier to make a completion. I tend to believe the latter, which means even average QBs can run a decent passing offense.

On a league basis, there has been no suffering of rushing totals in favor of passing. It is only our perception as Steeler fans because of the loss of Bettis and our emphasis on the pass. We have discussed the merits of this change ad nauseum here....