Cousins is 10th in the league in scoring, Al Jefferson is 12th, and Anthony Davis is 16th. All are over 20 a game and all are in their prime or no where near their prime. Brook Lopez finished 10th in scoring last year and is obviously hurt this year. Dwight has had solid scoring seasons. Guys like Aldridge and Duncan have numerous seasons over 20 a game and while technically PF's have games more like traditional centers (Blake Griffin is in that mold as well).
Frankly, that isn't much different than most years. Take 86-87, Moses Malone at 9th, was the only center in the top 11 in scoring that year. Hakeem was 12th, but there were no other centers in the top 20. How about 96-97, Shaq was 4th, Hakeem was 8th, and Ewing was 9th, but there were no other centers in the top 20. In 02-03, Shaq was 4th and he was the only pure center in the top 20 (Duncan, Garnett, and JO were in the top 20, but all were PF's that year). Even in the days of Wilt like 64-65, it isn't like centers were all over the scoring leader board. Wilt was 1st, Bellamy was 6th, Reed was 9th, and Thurmond was 17th.