Limit switches are usually wired Normally Closed (NC) this way if something happens to the wiring ( a break or disconnection) the machine will stop. If wired Normally Open (NO) the controller will not react to a broken circuit.
The touch plate would be wired Normally Open and use the probing routine. See this thread for a neat application: http://www.cnczone.com/forums/showthread.php?t=56079 (XYZ Probe modification)
http://pminmo.com/home-and-limit-switches is a good article about limit and home switches. If you go to the home page: http://pminmo.com, there is an articles section that you might find interesting.
What type of controller are you using?