This New York Times reporter compares the speeches of Sarah Palin and Barack Obama, finding similarities as well as differences. The main difference was the tone:

Where Ms. Palin was direct and forceful, Mr. Obama was soft and restrained. Where Ms. Palin was accusatory, Mr. Obama appeared to go out of his way to avoid pointing fingers or assigning blame. Where she stressed the importance of fighting for our different beliefs, he emphasized our need for unity, referring to the “American family—300 million strong.”

Gee, I wonder why the tone differed. Has Obama been accused of causing (or contributing to) the tragedy? If he had, you can be sure he would have used a different, more belligerent tone, the one we see whenever he is criticized. When you're accused of something you didn't do, as Palin was, you defend yourself. The only similarity I see between the speeches is that they were delivered on the same day.