Unlike John Kerry four years earlier, Barack Obama comfortably carried Catholic voters by 9% in the 2008 election. But judging from the howls and catcalls from hard line conservatives and anti-abortion activists over the invitation to President Obama to deliver the commencement address at Notre Dame, you'd never know he was the choice of Catholic Americans last fall.
In a letter to Notre Dame president the Reverend John I. Jenkins, the National Right to Life Committee (NRLC) called on the private university to rescind its invitation to Obama for the commencement in May. Not content to brand Obama the "Abortion President," NRLC vice president Anthony J. Lauinger protested:

"As a Notre Dame parent and supporter, I am outraged by this invitation to Barack Obama. I have apologized to my eight children for the poor guidance I provided them when I encouraged them to enroll at Notre Dame."

While the Lauinger octo-brood apparently voted for John McCain in 2008, a majority of their fellow Catholics did not:

Obama's solid margin came just four years after George W. Bush topped John Kerry by 52% to 47% among American Catholics. And that seismic shift in the political preferences of the Catholic electorate may be behind the vitriolic response to the specter of the President of the United States addressing the graduates of an elite American university. When Kathryn Jean Lopez of the National Review blasted the decision of Notre Dame administrators as "shameful" and protested "they took a giant step away from their identity as 'Catholic,'" she might as well have speaking about Catholic voters who rejected her candidate and her party.
Of course, the outrage at Red State, NRO and convert Newt Gingrich may just reflect the unfulfilled desire that only Republicans be allowed to speak at Catholic universities. As FireDogLake noted, Lopez had no issue when Condoleezza Rice, the pro-choice saleswoman of the Iraq war opposed by the Vatican, received an honorary doctorate from Boston College:

"I don't think BC is compromising any fundamental values by having her [Rice] speak."

(As it turns out, the "mildly pro-choice" Rice graduated from Notre Dame in 1975 and delivered the commencement address there in 1996. In 2005, she told the Washington Times, "We should not have the federal government in a position where it is forcing its views on one side or the other.")
In all likelihood, most Catholics would assume that exposing students to the political leadership of their nation, regardless of those leaders' views, fits within the mission of the country's premier Catholic university. Regardless, while they probably don't agree with all his views, American Catholics voted for Barack Obama just the same.
UPDATE: For some background on the history of commencement addresses at Notre Dame, consult Go Forth and Do Good: Memorable Notre Dame Commencement Addresses by Rev. Wilson D. Miscamble, C.S.C., professor of history at the University of Notre Dame and rector and superior of Moreau Seminary. The book from Notre Dame Press includes 24 notable graduation speeches from presidents of both parties as well as a litany of figures who no doubt found themselves on opposite sides of the abortion issue:

Among other featured Commencement speakers are: Joseph Kennedy, Sen. Daniel Patrick Moynihan, Andrew Young, Cardinal Joseph Bernardin, Condoleezza Rice, Kofi Annan, and Presidents Eisenhower, Carter and Reagan.