Which markup language is right for Internet telemetry?

Kelly McNeill writes “HTML is simple and XML promises flexibility, but can we afford the overhead of either? To be sure, the use of the Internet to transport data over long distances lowers the cost of operating a remote monitoring and control (telemetry) system by replacing the long distance telephone (or dedicated line) charges with an ISP subscription. As ISP subscriptions provide unlimited access for a fixed fee, there is little pressure to minimize the amount of data transmitted. However, as metered usage tariff systems come online for data services, we will be forced to reconsider this approach.”