It would have surprised me if President Obama didn’t receive more threats than Bush, Clinton, Reagen, etc. He’s getting the “normal” threats from the usual suspects (plain crazy people, unstable anti-government kooks, attention whores, people who think he’s “going too far” and those who think “he’s not going far enough”) and on top of that, a mountain of threats from racists who can’t handle having an African American president.
I expect, for example, the first female president, the first Asian American president or the first Jewish president will also receive an above average number of threats from specially bigoted crazies. I hope this will be avoided by the time those examples come to pass, and I hope this crap with Obama calms down.