There are many features of Google Glass that require an Android handset, namely GPS navigation and text messaging. However, according to a Google employee, Google Glass will be able to do all this with an iPhone as well. It's said that Google Glass will soon be able to function independently, regardless of of the device that it's paired to.
This means that users won't necessarily have to have an Android device in order to use Google Glass, and it's possible that they'll soon be able to function without needing the My Glass companion app. We already know that iOS doesn't take Google Glass lightly, and while the pair of glasses will at least work with the iPhone, users can't get turn-by-turn directions or use text messaging.
However, that's expected to change, most likely with the retail version of Google Glass, where it'll act independently instead of relying on your smartphone for a lot of its functions. Currently, Google Glass uses your Android smartphone's GPS and data connections to get many of the features working.
Taking into account what the Google representative said, it seems Google Glass will soon be fully functional on its own, and while you'll still be able to pair it with your smartphone, it shouldn't matter what smartphone you're using. However, it's possible that a companion app will always exist on Android that will give Android users a bit of an advantage over iPhone users, but we'll see.