Obito wanted to kill Kakashi, but make him suffer before that. That's why he first kicked and cut him and only then wanted to give a finishing blow, but Naruto saved him.
Kakashi on other hand doesn't want to kill Obito. He could have used Raikiri instead of a punch (but he still used a pretty strong punch, as it was enough to make Obito cough with blood right away).
Remember what Naruto said to Itachi? "I will protect the Leaf without killing Sasuke". Then in this chapter he said "Kakashi-sensei is just like me!".
Indeed, the same goes for Kakashi - he wants to protect Naruto but doesn't want to kill Obito.