The Doctor's Regeneration (theory)

Okay so we know the Doctor is still Mr. Tennant when hes finished regenerating, but why???

Well, I'm a BIG fan of the new series of Doctor Who, and I can't believe I DID NOT THINK OF THIS BEFORE! I had to get my sisters friend, to explain it to my sister, to explain it to me!
So the Dalek only hit the Doctor with a glancing blow,on his left hand side. So what does he do? He regenerates as we know at the end of the episode.

Lets track back to 'The Doctor's Daughter'. Jenny got shot, supposedly in the heart. And she regenerated as we can see, but she doesnt change her physical appearance. So maybe she just regenerated one of her hearts.

So we don't actually know how Dalek exterminations kill you (or at least I don't) so, we could conclude that they somehow affect your heart.

Now we all know that Time Lords have two hearts, so because the Doctor wasn't hit properly, it didn't affect him properly. So he does exactly what Jenny did and only regenerated one heart, and not regenerating properly, so his physical self is still the same.
Whether this affects the number of regenerations the Doctor has I don't know, but this seems the only plausible explanation for the reason he hasn't changed. And it doesn't explain the rumour that the Doctor splits himself into two people.

But meh.