"I applaud his desire to be the president of every citizen," said Warren, who has reportedly turned down at least 100 requests for interviews, including one by ABCNews.com.
And Robinson echoed last week, "Frankly, I think it is a magnificent, symbolic statement that Rick Warren and I will be praying for the new president and the nation. I think that's fantastic."
Gay activists said it was "heartening" to know that Robinson was included in the festivities, though his prayer wasn't televised in the live HBO special. But they are still uneasy about Warren's invocation, knowing the "symbolism" and "high profile" of that role.
"We are cautiously optimistic," said Joe Solmonese, president of the Human Rights Campaign, the nation's largest gay rights group. Ultimately, he said, Obama is a friend of the lesbian, gay, bisexual, transgender community. . "The idea is that there is a place at the table for everybody, but at some point we draw the line, when you bring in people with incendiary views that say derogatory things about some Americans," he told ABCNews.com.
Some believe that Warren's centrist views -- supporting a broader agenda for evangelicals than hot-button issues such as abortion and homosexuality -- might shift him to closer association with Obama.
Unlike ideologues like Jerry Falwell or Pat Robertson, Warren has talked about a loving Jesus, taking on causes like climate change, Third World poverty, sex trafficking and HIV/AIDS.
As leader of a 20,000-member mega church, Warren says some issues are non-negotiable: abortion, gay marriage, stem cell research, human cloning and euthanasia.
This tempest in the Christian teapot over the invocation has no precedent.
George Washington never had a prayer at his inaugural. It wasn't until 1937 that the invocation became tradition. Franklin Roosevelt asked a Catholic supporter of the New Deal to join a Protestant in prayer. Later, President Harry Truman added the first rabbi; and Dwight Eisenhower invited a Greek Orthodox minister.
Jimmy Carter cut it back to a Protestant and a Catholic. Ronald Reagan had only a Presbyterian at his first inaugural and later added a Catholic and a Jew. George H. W. Bush and Bill Clinton had Billy Graham, with Clinton adding another Baptist in 1997.
Prayer should be as "inclusive as possible," according to Reese. "The minister leading the prayer should not deny any aspect of his faith to please others, but he need not have every aspect of his faith expressed in his prayer."
The evangelist Graham never mentioned Jesus in his inaugural prayers.
Today Americans are divided over issues like abortion and gay marriage -- rather than the fear that dominated the presidency of John F. Kennedy, a Catholic, "over the Pope to run the government," said Reese.
By extending an invitation to both Warren and Robinson, Obama is "trying to reach out to all sorts of people, and some of them don't like each other," said Reese.
"Warren and Robinson won't find common ground on abortion or gay rights, but Obama can bring them together in concern for the poor or health care or doing something for the victims of AIDS in Africa," he said.
In the two years since Obama has been invoking a message of common ground, a group of disparate voices that includes progressives and evangelicals has been shaping a shared agenda on social issues.