That's just to cover their butts for international orders as customs. I'm pretty sure their wont be any extra charges as I've never had any. I've also seen US online stores say that I'll need to pay taxes in my country which I've never had to pay. It's probably a standard clause where this is the case in certain countries. But generally it must be large items.

Also this isn't shipping. This is on top of shipping. If they are saying this is shipping then that's a bit dodgy.