Why should they have one?
If used at home it's connected to your amp and there you have a headphone connector.
If used in the car you wouldn't be allowed to wear headphones. The sound of a car-hifi is better than that of a headphone.

I think I've read about someone connected a headphone via the line connectors there in this BBS. But I'm not too sure about that.

TeeMcBee
Got my Mk2! # 080000143