Blizzard define your realmList to a domain where your login server is located.
Luckily they prefix it, but they CAN use an IP directly breaking the code. It might also be different for Chinese servers.
For example
http://wowchina.com/ don't even use the prefix like the us/eu does, so keep this in mind. The Chinese realmlist is
cn#.grunt.wowchina.com