Here's a portion of the email I just received from his convention agent:
Jamie has been trying to get to Australia for a couple of years now. He was so looking forward to finally getting there and hopes the fans understand how hard everyone worked to make it happen, and have it in their hearts to forgive him and the promoters, but it just wasn’t meant to be.
I know how disappointing this is to some of you, but I expressed that given how hard he's worked in the past to make con appearances, we know this was something out of his power to make work.
I didn't receive word on James Callis, who is also scheduled to appear at these events, but there is a good chance he is also unable to attend.