I don't know for sure what part of the bbq lighters that altitude affects but I think it's the butane. I've tried a dozen different brands and it's always the same. We camp above 6k regularly and they won't light. I don't think it's the piezo that fails. Our camper stove has one and it works anywhere but it's lighting propane.
Just spent 4 days camping at 8800' and our BBQ lighter worked fine...
