I personally think that it all depends on what roles the actor does. I don't even think about Kevin Spacey being gay when I see him in a movie - but then again, he often plays characters who are a bit odd. I would find it more difficult to go and see him in a romantic comedy, playing the heart throb.
(I just want to say that I don't care if people are homosexual or not, it does sound a bit like that in the sentences above. I find that my vocabulary isn't good enough to express this with exactly the tone that I want in English.)

Since TC has chosen to do roles where he is either the gorgeous hunk (Top Gun for example), in a heterosexual relationship (Days of Thunder, Jerry MacGuire) or the Great Action Hero (Mission Impossible, Last Samurai) I think that it would have crushed his career if he would have admitted that he is gay.
Girls and women wants their movie hunks to be hetero so that we still can fantasize about them in "what-if-it-was-us" way and men who go to see action heros don't want to sit there and think "he's GAY"! (Big generialisation, but still.)

Just my two cents.