I've tried to found the answer too, cause not only you curious about this...me too. In fact if you notice, not only Filesonic, but almost major flehosting had same rules about Hongkong..here's ehat i've got from jdownloader forum ( only in this case, this person ask about Fileserve...and i copy you the interesting answer from one member there...)
Maybe since the Hong Kong is now officially part of the PRC (People's Republic of China) and due to the fact that they tend to block other sites outside of the PRC themselves and have forced Google to remove content and as such Google and other IP providers and sources do not wish to comply with such restrictions not to mention the Human rights issues in the PRC.
It is possible for whatever reason the PRC is also blocking certain sites and or routes out of China which may now also include Hon Kong.
It is very probably also in many places other ISP's or sites may be blocking access from china ISP's for same above said reasons and lets also not forget that the RPC is also one of the biggest attackers tryng to hack into or find vulnerabilities on foreign ISP's.
I personally am blocking not whole netblocks yet but do find I am blocking usually three to four IP's weekly that are out of the RPC as attempts are made of scanning and hacking into such things as sshd etc.
Yea occasionally I get some out of South America and Germany and Italy and Russia but those have dropped mostly over time as compared to the increase I see from the RPC.
Oh yea lets also not forget ACTA and it's impact it is having already even though it is not finalized completely yet, parts are being implemented as you read this.
Here's he link, in case you need to find out more...
http://board.jdownloader.org/showthread.php?t=21892
Well, only peoples from filehosting know the right answer, i just try to help you mate...
Regards