I reckon the ball swung about as much in 1999 - a pretty good summer - as it did in 2007 or 2008. Also, 2002 was almost as diabolical as 2007 or 2008, and 2004 was better but not by a huge degree. In neither '02 nor '04 was swing in the slightest prevalent.
It was noted by any number of county bowlers in early May 2001 (before the summer's opening Test when Dominic Cork, one of the best swingers of the last 15 years, failed to get so much as a single ball to go off the straight through the air) that the ball simply wasn't swinging that year. Everyone presumed something in the manufacturing process had changed, though Dukes never admitted anything, for obvious reasons. Then in 2007, they started to go properly again, and county bowlers noted this within a few weeks once more.
As I say, it'd be nice to blame the poor weather, but poor weather was certainly not unusual in some summers from '01 to '06. '03 and '06 were pretty good, and '05 was standard-fare. But this decade as a whole has been seriously schizo on the weather front in this country.