Doctor: Fear. Loneliness. They're the big ones, Rose. Some of the most terrible acts ever committed have been inspired by them. We're not dealing with something that wants to conquer or destroy. There's a lot of things you need to get across this universe. Warp drive... Wormhole refractors...You know the thing you need most of all? You need a hand to hold.
Rose: [Seeing cat.] Oh! Aren't you a beautiful boy?
The Doctor: Thanks. I've been experimenting with back-combing...oh.
Rose: [Seeing him grimace.] What?
The Doctor: Nah, I'm not really a cat person. Once you've been threatened by one in a nun's wimple, it kind of takes the joy out of it.
The Doctor: Nobody else in this entire galaxy has ever bothered to make edible ball bearings, genius!
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.