Many people ask the question, in relation to machine-to-machine and SCADA, where do these fit into the scheme of things? They are effectively elements of the Internet of Things. Machine-to-machine communications, typically used for business-to-business functions and for relatively high-cost deployed devices. Fit in, there's a subset of the overall Internet of Things.
In relation to SCADA applied in the industrial environment, there is indeed an overlap. The Internet of Things can expand the scope of SCADA down to much lower-cost deployed infrastructure, back to your powered devices, for example, to extend and enhance its capability.
The main difference of IOT is that it is extending internet connectivity to billions and in fact tens of billions of low-cost, low-power devices, hence providing connectivity in places where it has yet to be economically viable or even achievable.