Virtually every country on earth requires a ticket back. Surprisingly, China is ok with a one-way ticket.

http://www.delta.com/planning_reserv...tion/index.jsp

Assuming you had a visa, you had everything in order. It is true that if you are refused admission, the carrier you came with is responsible for taking you back, but it was a pointless question because even if you had no return your carrier could not deny you boarding.