You have an iPod, what do you listen with? You have an iPhone, what do you listen and make calls from? Apple's headset and/or head phones.
In the 2002 article Mind your language, by Game Developer Ben Cousins, Cousins explains what to focus on to make a successful product. In short: whatever the user spends most time with. Apple is usually great at this but seem to be missing the headsets.
It's not that the headsets / head phones are bad per se. They just aren't really good. And the quality is awful, I'm on my 6th pair this year and mad as a hat when the sound goes in one ear.
Apple should really look into making a better headset, ensuring that customers are using headsets with the intended functions.