Now that the episode has been (legally) viewed by both British and American audiences, Doctor Who producer Russell T. Davies has taken the time to explain just what was behind that last minute cameo from an unexpected but familiar face in the first episode. Unsurprisingly, said explanation suggests that Mr. Davies is entirely unfamiliar with the concept of "rumor" versus "fact".
In his regular column in the UK Doctor Who Magazine, Davies wrote about the surprise appearance of Rose at the end of season four's first episode:
When I wrote the very first draft of 'Partners In Crime' in September, I just got the devil in me. What if, I thought, what if we could transmit something, just once, that no one sees coming...? ...This is Donna's series, and if anyone had caught a rumour of Rose's return, there was a genuine danger that Catherine's launch could have been overshadowed. We owed it to her to carry this off successfully.
'Dr Who' boss explains shock Rose cameo [Digital Spy]