The wound is wrapped with sphagnum and covered with a plastic cover and tied. Eventually roots form where the wound is, fill the sphagnum and then the branch can be cut and planted as a seperate plant. Vines however are a different matter. This protects a climbing plant from total damage and stem death as it is bent, kinked or banged about along the host plant during wind or falling limbs. Therefore I think what is happening in Nepenthes is that you cannot completely cut off the phloem and initiate root development.
Simple cuttings are general propagating material but there are a few things to consider.
There are two basic types tip and lateral. Tip are mearly the very ends of the growing plant. Since they are soft new growth it is best to leave 3-5 leaves on this type. Lateral cuttings are any cuttings that are not tip cuttings, i.e. cuttings lower on the stem. New growth points or nodes, are above each leaf, the portion between them are the internodes.