In games, for example, it's pretty common for bandwidth to be tight enough that a useful optimisation is quantizing floats down to shorts (which is good enough

In games, for example, it's pretty common for bandwidth to be tight enough that a useful optimisation is quantizing floats down to shorts (which is good enough for e.g. quaternion representation of weapon direction). In that environment, the idea of using XML or JSON is ludicrous. (i.e. the Web is not the Internet)