As a response to 7, 10 was holding it in so he could see all his companions again as himself and could do no longer when he reached the TARDIS. The build up of energy made it explode out of him whereas with 9 he just let it happen.
Doctor Who Challenge Day 1: The Tenth doctor is my favorite. I absolutely <3 Nine and Eleven, but Ten holds a very special place in my heart. He's compassionate and loyal and genius and caring and loves so much. He carried so much love in those two hearts, but also pain, and my heart hurt when his two hearts did. And, you know, Ten's hair is brilliant, and he's "slim and a little bit foxyyyy!"