They're usually the same, just shaped differently to be used most easily. But there are different wax types in general, like for sensitive skin or whatever. Use more sensitive wax on lip/bikini line, and make sure you've got the right shape.
I don't know, but i think so because when you buy them sometimes it says, for face only or stuff like that. Im not 100% sure, but im guessing their is a difference.
My guess would be that they're just different sized strips for different sized areas.