Take it easy buddy. If you're a dick everytime someone tries to be nice, people won't be nice to you for long. Just because you're riding up with someone you don't know doesn't mean you don't have any friends.
That said, occasionally I ski with headphones, but pretty rarely. I think the biggest concern is the safety issue. Especially when it's crowded, you need to be able to hear and register what's going on around you quickly enough to react. When I do ski with my music, I make sure that, while I can still hear the music well, I can also hear what people say to me and the sound of my edges on the snow. This makes it easy to avoid incidents and still be courteous to others. I've found that I don't like having music when I am with friends for exactly the reasons CGM stated. So I typically end up only listening to music when it's one of those easy going days that I'm skiing alone.
"The world would be a better place if everyone kayaked."-Brad Ludden (Valhalla)
"You only get one chance to run a drop blind."-DD