I think it's different design approach adpopted because limits of computational power at the time means they have to carve the F-117 up into sizeable blocks and look at the combined effects from them.
General 徐光裕 revealing some tid bits:
-PLA is certain to reduce to 1.5 million by 2020, with ratio of Army (inc. 2nd Art.): Navy : Airforce as 5:3:2.
They would all be modernised force.
(me thinks by 2020 China would have enough budget to maintain a 1.5 million completely...