An IoT network consists of many devices, which might not be at the same firmware revision. Upgrades might be spread out in time because the hardware might not be physically available and so on. This makes compatibility at the interface level important. Since small networked sensors might be memory and processor constrained, versioned binary protocols or simple REST protocols may be preferred. Versioned protocols are also useful in order to allow things with different hardware revisions to communicate at different versioned end points.
Massive sensor deployments can benefit from less talkative protocols and layered message queuing architectures to handle events asynchronously.