Wayne,
I don't know exactly why, however it was marked as double rankings since at least January, and I think it was when the 2006 Tournament Calendar first came out on the TBA website.
If you have a look, NSW Open at Mt Druitt is also being allocated double rankings points.
As to the actual reason why, I do not know. Extra incentive for people to travel I guess!
On Edit:
PS - This is Easy Tiger (Tim) not Feral.. forgot to sign out of his account.