In the commentary, the director says that the voice sounds like that because he wasn't allowed access to any old Dalek voice recordings, and he didn't have any old Dalek episodes with him to watch for comparison, so he did the voice himself from memory. Poor memory, it would seem.

I'm not going to be changing anything about the film itself for this disc. However, now that I've got the whole movie running at the proper speed, a fan edit might be on its way after the standard release...

--edit--

Oh, and which one of you is ugnaught over at /r/doctorwho?