My daughter is vegetarian. We always cook her vegetarian food for dinner. Her little brother likes to bug her about it. We tell him not to, because giving people a hard time about their preferences is rude and annoying. But we also make sure that the vegetarian can't get cranky when everybody else is eating real bacon and she's eating vegetarian bacon. That'd be just as rude and annoying. It's called "tolerance", kids. I don't understand how we've entered into this world where we aren't all supposed to try to tolerate (let alone encourage and support) one another, but that tolerance only goes in one direction. That seems very odd to me.
If you would still feel uncomfortable if it were a photo of man and a woman doing the same thing on your screen in your open office at work, then no. I personally wouldn't want either in my work environment. I have a strong separation of my personal life and work. It's a simple test really, just imagine the reverse and if you feel the same way about a naked man and woman on your desktop at work, then no, you aren't being a homophobe.
Though the U2 album has become such a meme, I'm sure people would have a good laugh at Apple over it.
As an added kicker, I stressed over it for a couple of weeks first, worried about whether I was being homophobic or not.