I agree with rhino, I think China and the U.S. had already started consultations before, it's mostly like Premier Wen Jiabao attended the United Nations conference in New York and met with President Obama to decide the deal.
First China want to buy C-130, and then Obama will write the letter to the Congress, if China does not want to buy it, how would Obama do this? He is the president, he is not a fool.
Y-9 just in assembly, flight test phase, It still needs quite more time to be mass production, China buy a batch of C-130, dosn't mean kill Y-9.
and this deal just the start, China will buy more U.S products,the U.S should not think China is the enemy.