Bowie's music is not "gay". It doesn't suggest changing your sexual preference from "straight" to "gay", rather it suggests breaking your "gender role" - dictated by the society in which you live. Basically, society tells you how to act if you want to be considered a "man" or a "lady". If you are a boy you have to do things that are considered "masculine", and if you're a girl "feminine".
Bowie was rebelling against conforming to a gender role. Others rebel about other things. Rappers rebel against police for telling them what to do, or how to live, or what drugs they use in their own homes. Bowie experimented with his gender all the time, while the rest of us need an excuse, like Halloween or Carnivale to dress up and act as a member of the opposite sex (with an opposite gender role).
To begin to answer the question of whether Bowie fans are gay, we should think about why Bowie=gay. There are gay men who shock us when they tell us they are gay. That is because their sexuality is homosexual, but they still conform to their gender role of acting like a "man". However, the most visible gay men are the ones that play with their gender as well, and act "feminine". From this stereotype we reason that feminine=gay. And because Bowie wore makeup, and society tells us that only women wear makeup, we reason that Bowie=feminine. We then derive that if Bowie=feminine and feminine=gay, then Bowie=gay. It's a TRANSITIVE relationship (go look it up at Dictionary.com). All of this reasoning, however, is incorrect. In fact it is completely ignorant.
If you are still confused, what I'm saying is that being gay has nothing to do with "acting feminine". So Bowie's "acting feminine" has nothing to do with his sexual preference. Furthermore, my listening to David Bowie does not make me anything that he is, anyway.
I'm bad at sports and I throw like a girl. But I'm sure about my sexuality -- I'm heterosexual.