Averages aren't everything. As I said, his figures at Headingley in 2006 flattered him greatly, there were just two out of six what I'd call "genuine" wickets (Taufeeq Umar and Younis Khan in the second-innings - the others were end-of-innings wickets or Inzamam falling on his stumps). Obviously his figures in the just-concluded Test flatter him enormously as he again picked-up end-of-innings wickets, and in his only other Test at the ground he bowled just 7 overs, being gifted another end-of-innings wicket, Bravo when he was swinging with the game gone.
He's only played 1 Test at Edgbaston, in which he took 3-80, 1 of which was a tailender. And at Trent Bridge, well, the wicket in 2006 turned, but still 3 out of his 5 were end-of-innings wickets. In 2007 he got 2 end-of-innings wickets to turn poor figures into decent ones, and in 2008 he bowled just 11 overs without a wicket.
I'd hardly call him a riproaring success at any of those grounds. It's only Old Trafford (25 wickets at 16.72) that he's had success at in this country.