TUIO (Tangible User Interface Objects) was used as the core of the touch processing, as it is "a common protocol and API for tangible multitouch surfaces" (tuio.org). Essentially, TUIO is a set of XML-based messages broadcast through UDP socket connections, which gives a clean separation between the touchscreen hardware and the user interface application.
For touchscreens which support TUIO directly like some PQ Labs touchscreens and DIY screens based on the Community Core Vision (CCV) or Touchlib libraries, the bridge was unnecessary and the touchscreen directly sent TUIO messages to the npTuioClient plugin.
I hope you found this information useful. Thanks to Kent and Torin for sharing it with us!