Continuity mistake: As the Doctor is being put to sleep, he lies on the operating table which has no pillow for his head. When Salinger uses the defibrillator on the Doctor, he has a blue pillow cushioning his head.
Continuity mistake: When Dr. Holloway asks for the scalpel in the operating room, her gloves are tucked into her surgical gown sleeves, in another shot, the gloves cover the ends of her gown sleeves.
Continuity mistake: When the Doctor wakes up and screams from the shocks, the tube pops out of the mouth tube. In the next shot, when the Doctor falls dead, the tube is reattached to the mouth tube.
Continuity mistake: When Grace is operating on the Doctor, the tray holding the surgical tools is at the end of the operating table, in the next shot (from an aerial view), you can see that the tray is over the Doctor's feet.
Continuity mistake: When they wheel the Doctor into the emergency ward, Wheeler grabs onto the stretcher and helps pull it, in the next shot it's just Bruce and the other paramedic moving the stretcher.
Chosen answer: Whereas Grace and Chang are both human, Captain Jack Harkness is alien - So the effect the TARDIS has is very different. In addition, as is revealed in the series as well, The TARDIS is more than a machine, it is alive... It also has knowledge even the Time Lords do not have - By making Jack Harkness immortal, it is also fulfilling his destiny.
Phoenix2312