I wonder why as well, I installed the Canadian Nissan Version ( my parts guy cuts me a rate now, so it came out cheaper ), we don't get the stifffeners, ( not like the directions from xterraparts anyway, we get oversized "L" brackets ).. from what I've read, something like the U-haul type, yet its still a Nissan part. Still class III, which means 5000 towing.
The install was removing the bolts to the bumper, but not the bumper itself.

------------------
http://www.soxc.org
http://www.geocities.com/x_canuk