Rear Upper Control Arm Torque Procedure

I plan on replacing my rear upper control arm this week and I was looking over the factory service manual on how to remove and install the arm.
It doesn't seem too difficult (assuming everything comes apart easily) but I had a question on the installation portion of the documentation.
It says to install the mounting bolts in the bushings and torque while the vehicle is still in the air.
Here's the exact instructions,

INSTALLATION
(1) Position the upper suspension arm in the
frame rail brackets (Fig. 10).
(2) Install the mounting bolts and tighten to 100
N·m (74 ft. lbs.).
(3) Retighten the heat shield back into place.
(4) Pull the arm down on the differential housing
bracket and install the pinch bolt and nut. Tighten
the nut to 95 N·m (70 ft. lbs.) (Fig. 7).
(5) Remove the supports and lower the vehicle.


My understanding is that bushings should always be torqued while the vehicle is on the ground with weight on them so they don't tear or prematurely wear.
Any thoughts on what I should do here?
I'm leaning on torquing the bushings with the vehicle on the ground but I'm assuming the service manual tells you to do it in the air for a reason.

You are quite right for normal bushes, unfortunately when they designed the upper arm they put the bushes in the wrong plane for some reason, so clamping on or off load makes little difference, movement eventually just pulls the bush to bits.