At face value, the lyrics would seem to be about a woman's dysfunctional relationship with a guy like this:

http://www.youtube.com/watch?v=fxrd_jZJxkg

But I really don't think so ... unless we could say Henry Rollins in the video above is a personification of the music industry, and her status as a pop culture icon :-)

Worth noting right away is that Madonna did not write this song herself ... it is actually attributed to four composers and she is among them. But to examine it, I will take into account that it is Madonna who co-wrote (maybe) and chose to perform it, and therefore felt a strong enough affinity with it that she wanted to include it on her album. And it's worth noting that she put it on an album where she chose to portray herself on the cover (at approximate age 50) as:
http://www.mad-eyes.net/disco/hard-candy/images/album_400x400_hardcandy.jpg
:-)
I think a lot of times artists compose lyrics that appear to be speaking to or about a person they are in a romantic relationship with, but in fact they have directed the words in the song to themselves--and they may not even be about any particular relationship with another person. I think that is the case with this one, at least re: Madonna's choice to sing these words.

Through the years, Madonna has built a career upon the persona of a sexy, powerful/dominant, agelessly beautiful pop icon who craves success and sends a "go for it, whatever 'it' is for you" message to the masses. In this song, I see her addressing that part of herself, and perhaps wondering if she is a slave to this Dominating Winner that she has created herself to be in the public eye. The lyrics seem to be at times directed to her own persona, and at other times to the masses (perhaps wondering if she will be able to win them over again this time around).

In the Rolling Stone review of the "Hard Candy" album, Caryn Ganz wrote: "Dominance isn't just a fetish for Madonna, it's her religion. It's no accident that she opened each show on 2005's Confessions on a Dance Floor tour by clenching a riding crop in her hand, jerking a gagged male dancer around by a leather leash. And she never puts down the whip: Since 1986's True Blue, Madonna has claimed writing or production credits on every one of her songs, even when she worked with dance-music artists such as William Orbit, Mirwais Ahmadzaï and Stuart Price. So it's surprising that her eleventh studio album — her final one for longtime label Warner Bros. — is an act of submission. For Hard Candy, Madonna's midlife meditation on her own relevance, she lets top-shelf producers make her their plaything. "

... So yeah, I think "Voices" is a message about dominance and submission in the music industry (and how her public persona relates to her own self-image), not the bedroom :-)