I'm not sure that PPIMan is quite right. It's not a case of Cat II/III needs LVPs - I think it's operations below a visibility at which the controller in the VCR can see enough to control what's going on.
In addition, any airport that wants to operate below a certain vis (400m I think) must have LVPs. The procedures are meant to protect the runway from errant aircraft and vehicles etc. it's not just an ILS thing - aeroplanes taking off deserve protection too!