"I assume you mean that your IP address changes from time to time. The Access Key solves that problem. Our server keeps track of your IP address."
This specific issue I could solve with dyndns ... but the other problem I'am trying to argue you're still missing, maybe cause it's to Americans not so obvious:
Most people using 3G USB Sticks, wired internet seems to loose market. Public IP4 addresses are rare, therefore Internet providers (most) hold each customer in a private IP space. If you need a public IP you either have to pay for it or ask if your provider can spare one, otherwise you won't get one.
Access from outside is not given "naturally".
Such services might make sense for us European using IP6. But still it's to the providers how they design their network. Maybe they do it similar assigning only private address space to customers.
Well there is a benefit: you'r not vulnerable to direct service attacks, at least as long as the attacker is not sitting in the same private address space.
Even If I would have a public IP at home, it would be no use for me. In the company I'am working the only port outside is 80. Pages like Youtube, Twitter, Facebook etc. are blocked. Who cares - I don't have an account in either of them. Do you think I'am old? No: I'am 36 and feel no need to be permanently online ... why should I be at home?
Hope this clears things up.
thomas