Ed, you are correct. I was referring to new production forklifts.

I am pretty sure Jeff is speaking in reference to the "new forklift" subject heading, as far as operator _presence_ systems go.
While every truck, even older ones, should by now be fitted with an operator _restraint_ system, it is new trucks that will have the -presence- system.

Yes, from a manufacturers stand point it is mandatory in the USA.

The industry standard for industrial trucks, sold in the USA, (and a placard is attached to each new truck stating this) is the "b56" standard. Older trucks were covered by the ASME b56.1, and since about 2004, the "Industrial Truck Standards Development Foundation (ITSDF.org) has taken over the responsibility of upkeep and update of the standard.
You can download the standard from the ITSDF.org website for free.

i cant answer that bbforks
i cannot speak for the manufacturer

but it is of MY opinion they are putting these "safety" features on these machines for a specific reason. My best guess would be they are doing it in response to the number of accidents that happen from unattended machines that are reported to OSHA every year due to operator negligence. I'm sure there are other reasons though. But as i said.... its just my best guess :o)

so from a safety standpoint i would say it might be mandatory...

Is it mandatory for the manufacturer to offer it?

yes
if the truck is designed with it and it comes on the truck from the manufacturer then yes it is supposed to be on the truck and required to work as designed.
it is part of the safety system designed to disable functions if the operator is not present in the seat.