so they can charge what they want
I agree with you that they can charge whatever they want for anything they have. Airlines can charge baggage fees, and hotels can change "resort fees" (even if you're just using the room). However, that doesn't mean it will annoy some people. It's my preference to get one charge for tanks and weights. Folks that can put lead in their luggage (which I might do when I visit) may be happy with their pricing schedule. Just not me.