Iowa has never been a particularly kind state to the Clintons. It was the one and only state in the nation in which Clinton in 1992 did worse than Dukakis. Neither Bill in 1992 or Hillary in 2008 won the caucuses there, of course (though Harkin's favorite son candidacy helps explain Bill's loss).
But yeah, along with Wisconsin and Minnesota, another state where Obama clearly is the stronger candidate.
Other states where Obama is stronger: Washington St, Oregon, Nevada, Colorado, New Mexico Virginia, and New Hampshire... granted, he is weaker in Ohio and FL, but Hillary wouldn't win them anyways