Diana Ross, Quincy Jones, Diane Sawyer, Iman and Ashford and Simpson were among those who helped Oprah Winfrey celebrate the first anniversary of her successful magazine, O, Tuesday night in Manhattan, reports PEOPLE. "I just came to party," the hostess and media magnate, 47, said several times. Of her publication, Oprah said: "Acclaim and profit are nice, (but) what means the most are the readers themselves . . . My goal with this magazine was to let women know that they are okay. They don't need another lipstick, or pair of shoes or the perfect outfit. All you have is within you." In her speech, Oprah thanked her "life partner of 15 years, Stedman Graham" -- then went on to explain that he would be ducking out of the festivities early because he had to teach a "Dynamics of Leadership" class in the morning. As Oprah assured the crowd, "If you see him leave early, he isn't mad or anything."