Actually the iPad does have USB host - people have been using the camera connection kit to connect keyboard, usb keys, etc.
However, Phidgets are NOT supported. Apple does not allow direct access to attached USB devices, so there is no way to support directly attached Phidgets on an iPad. If you would like to attach Phidgets directly to a tablet, we fully support Android tablets.
iOS only allow connection to remotely attached Phidgets via the webservice.