I answered this via email, but I am posted it here now for visibility:
The services within ThingWorx may just perform local functions like updating local properties in response to scheduled events, for instance, or, they may perform REST or socket operations to remote sources to obtain information or distribute updates. These remote devices can be anything from computers or raspberry pi’s to tractors or vending machines. So you can sit down and write a service on the ThingWorx server which can then be passed to any connected remote device in the network. You can trigger a service on the Platform in a mashup, and wind up with a website view that has data from devices on the other side of the planet, all in an instant. IoT web services are basically web services which are able to easily traverse network connections to many, many devices at once.
So really, the difference is not in the services themselves, but in the framework upon which those services are run. An IoT application like ThingWorx has the network framework already in place to handle vast amounts of requests with relatively the same amount of work that it would take to ping a regular web server for some kind of JSON information. You can build one REST request, and quickly ensure all of the remote devices connected to ThingWorx respond to this same request with particularly formatted data which is easily processed and displayed graphically.