The United States had hoped that Bhutto, armed with a strong election mandate, might have been able to forge a power-sharing accord with Musharraf, who has just embarked on a second five-year term as president, taking office after a vote by lawmakers that was sharply contested by his political opponents.
Husain Haqqani, the director of the Center for International Relations at Boston University, said Pakistan's dynastic traditions probably drove the decision to anoint father and son.
"Politics always has a sentimental dimension all over the world," he said. "It is the reason the Kennedys and the Nehru-Gandhis get elected."
Ayaz Amir, a columnist for the Dawn newspaper, said the accession of Bilawal Zardari and his father had "feudal" overtones.
"It doesn't reflect well on our politics, but that was the compulsion the People's Party faced," he said. "It's an effort to keep the Bhutto mystique alive."
At Sunday's news conference in Naudero, in Sindh province, the elder Zardari demanded a United Nations investigation of the assassination.
Bhutto's party has sharply disputed the government's version of events surrounding the attack against her, particularly the contention that she was not killed by an assassin's bullets. The government said she died of a skull fracture after hitting her head on the lever of the vehicle's sunroof as a suicide bomber struck.
Bhutto aides who viewed and washed the body said gunshot entry and exit wounds were clearly visible, and opposition lawyer Athar Minallah, a member of the board of the hospital where she died, asserted that doctors were pressured into silence.
The Dawn television station late Saturday aired previously unseen amateur photos of the assassination scene, showing a clean-shaven young man in sunglasses aiming a gun at Bhutto's back. Just behind him is a man wrapped in a white shawl, believed to have been the suicide bomber.
Times staff writer James Gerstenzang in Crawford, Texas, contributed to this report.