[dns-operations] strange policy on amazon DNS setting

[Robert]

Hi,

 From a host within China I got the NS records for amazon.cn,

amazon.cn.              499     IN      NS      ns4.p31.dynect.net.
amazon.cn.              499     IN      NS      ns1.p31.dynect.net.
amazon.cn.              499     IN      NS      u2.amazon.com.
amazon.cn.              499     IN      NS      ns1.dynect.cn.
amazon.cn.              499     IN      NS      ns2.dynect.net.cn.
amazon.cn.              499     IN      NS      ns2.dynect.cn.
amazon.cn.              499     IN      NS      u5.amazon.cn.
amazon.cn.              499     IN      NS      ns2.p31.dynect.net.
amazon.cn.              499     IN      NS      ns3.p31.dynect.net.
amazon.cn.              499     IN      NS      ns1.dynect.net.cn.

But from a host out of China (the US) I got the results,

kindle.cn.              900     IN      NS      u2.amazon.com.

(only one NS RR)

How and why does amazon's DNS setting behave as this? Thanks.

robert.