The longer torch body is a traditional design that is designed to replace machine versions of oxy-fuel torches on industrial cnc machines. It is designed to fit in the same torch holder, and the long length is because the oxyfuel torches are pretty long as well.
The new short torch design is for more modern, low profile entry level machines, and it does not have the rack gear that is on the longer torch. I suspect it is the best choice for most newer machine designs.
This torch ws just introduced with the new Hypertherm Powermax65 and 85 machines and can be seen with this link:
Powermax65 Mechanized Plasma Cutting | Hypertherm