There is more to it than just the brand of ball - though that obviously is a big factor.
Anderson is a bowler who relies heavily on swing and although the Duke may swing more, the conditions in Australia are not as conducive to swing as other parts of the world. This is well illustrated by looking at the Test performances of another fine swing bowler - Australia's Terry Alderman. In England, where he played 12 Tests, he averaged 19.3 while his 20 Tests in Australia yielded 15 fewer wickets at an average of 29.4 . Furthermore, his other 9 Tests (played in New Zealand, Pakistan and the West Indies) yielded 19 wickets at 52.3 . Horses for courses!!
The fact remains that James Anderson has taken more wickets than any other pace bowler in the history of the game.
It's a pity that Anderson's critics can't show the same good grace as Glenn McGrath (whose record Anderson broke) when McGrath said. “If he can raise the bar to 600 wickets, that's an incredible effort. I was proud to hold it for as long as I did - for it to be beaten by somebody like Jimmy Anderson is great. I have a lot of respect for Jimmy. He's been an incredible bowler for a long time. To have played well over 140 Tests and just keep running in, day in, day out, and remain at the top of his game, I'm very proud Jimmy's got there. When it comes to the art of swing bowling, there is no-one better.”
In turn, Anderson was humble after breaking the record, acknowledging McGrath as a far superior bowler.
Anderson has achieved what he has through hard-work and dedication. He will never be regarded as good as some of the great fast bowlers but he has been (and might continue to be) very, very good.