The Doctor: I'm not... I'm not... I'm not from Mars!
Mr. Copper: To repeat, I am Mr. Copper, the ship's historian, and I shall be taking you to old London Town in the country of UK, ruled over by Good King Wenceslas. Now, human beings worship the great god Santa, a creature with fearsome claws, and his wife Mary. And every Christmas Eve, the people of the UK go to war with the country of Turkey. They then eat the Turkey people for Christmas dinner, like savages.
The Doctor: Excuse me, sorry, sorry. But, um, where did you get all this from?
Mr. Copper: Well, I have a first class degree in Earthonomics.
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.