Winfrey tells "Extra" that Cruise and Holmes "had a limited number of people that they could invite." She says, "That's fine. I don't get invited to everyone's wedding."
The 15th-century castle in Italy where the ceremony is expected to take place can fit 1,400 people.
Winfrey says there are no hard feelings. She says she still plans on buying them a wedding present.
Odescalchi Castle near Lake Bracciano — the likely venue for the weekend wedding of Tom Cruise and Katie Holmes — has attracted other celebrities, though, including CNN foreign correspondent Christiane Amanpour and Italian pop star Eros Ramazzotti.
Cruise, 44, star of the "Mission: Impossible" movies, landed in Rome with some 10 people Monday.
Local officials and residents have remained tight-lipped, and Bracciano Mayor Patrizia Riccioni would only say she received a request to clear the square in front of the castle.
When Amanpour married then-U.S. State Department spokesman James Rubin in August 1998, about 180 guests, including John F. Kennedy Jr., attended the reception at the castle.
Earlier that year, Ramazzotti married TV hostess Michelle Hunzicker in Bracciano, gathering a crowd of pop and TV stars, including Tina Turner and motorcycle racer Max Biaggi. The reception was held in the castle.
Having once hosted princes and popes, the imposing residence is now used for conventions, gala dinners and receptions. The castle boasts six towers, halls, gardens and a chapel nearby. Its museum, featuring frescos and ancient furnishings, is open to the public.
Cruise and Holmes, 27, became engaged in June 2005. They have a daughter, Suri, who was born April 18.
Holmes, who starred in TV's "Dawson's Creek," was previously engaged to actor Chris Klein. Cruise, an Oscar nominee for his roles in "Born on the Fourth of July," "Jerry Maguire" and "Magnolia," was previously married to Mimi Rogers and Nicole Kidman.