The Christmas Invasion - S2-E2
Doctor: These human beings. Consider their potential. From the day they arrive on the planet and blinking step into the sun. There is more to see than can ever be seen. More to do than - no, hold on...Sorry, that's 'The Lion King'. But the point still stands. Leave them alone!
The Christmas Invasion - S2-E2
Doctor: See, there's the thing. I'm the Doctor, but beyond that, I - I just don't know. I literally do not know who I am. It's all untested. Am I funny? Am I sarcastic? Sexy? Right old misery? Life and soul? Right-handed? Left-handed? A gambler? A fighter? A coward? A traitor? A liar? A nervous wreck? I mean, judging by the evidence, I've certainly got a gob.
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.