The Impossible Planet (1) - S2-E11
Doctor: Pfft... I'd have to settle down. In a house or something, a proper house with... With... With... With doors and things. Carpets! Me! Living in a house! Now that... That is terrifying.
Rose: You'd have to get a mortgage.
Doctor: No.
Rose: Oh yes.
Doctor: I am dying. That's it. I am dying, it is all over.
The Impossible Planet (1) - S2-E11
Doctor: So, when it comes right down to it, why did you come here? Why did you do that? Why? I'll tell you why. Because it was there. Brilliant. Excuse me, ah, Zach, wasn't it?
Zach: That's me.
Doctor: Just stand there, 'cause I'm gonna hug you. Is that all right?
Zach: I s'pose so.
Doctor: Here we go. Coming in.
[He hugs Zach.]
Doctor: Ahh, human beings, you are amazing! Ha!
[He releases Zach.]
Doctor: Thank you.
Zach: Not at all.
Doctor: But apart from that, you're completely mad. You should pack your bags and get back in that ship and fly for your lives.
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.