QNH is for TOD/Wind is for GS Mini
Besides the pressurization system, there is another reason, why the QNH is needed on the approach page:
During Cruise, you are normal flying with Standard Baro-Setting. So your height above MSL depends on the QNH of the region you are flying through. For the FMGS to be able to calculate the correct Top Of Descent, it needs to know the QNH of the destination airport. If there is a huge low-pressure zone at your destination, the descent from FL350 will be significantly shorter than with a high-pressure zone.
Besides the increase in VAPP for large head winds, the wind information is also used to calculate the Ground Speed Mini function. (See FCOM 1.22.30, somewhere around page 66)
For the temperature, I am not sure, it is probably for the descent performance calculation, also.
Hope this info helps.