Continuity mistake: During Donna and the Doctor's conversation with an Ood at the reception who she approaches to ask if he's all right with being a servant, in shots facing the Ood, he's holding his translator ball higher than he is in wide shots and shots facing Donna. (00:11:50)
Continuity mistake: After the Doctor and Wilf get off the seniors' bus, they're waving goodbye. In a close-up shot, the Doctor is waving with his right hand, but in a wider shot immediately afterwards, he's switched to his left hand. (00:25:10)
Continuity mistake: At the end, when the Doctor is watching his hand starting to glow, shots from his point of view show that he's holding it vertically. But shots from the opposite view show that he's holding it horizontally. (00:43:39)
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.