Just came across this thread and seeing as it's almost 2 1/2 years old it's probably long dead, but I'll throw my thoughts in anyway...
I thought this was a bit odd too, EVERY other car I've had goes down to 'LO' on the climate control (including my previous Primera). However when I thought about it a bit more it started to make sense... remember that the temperature you dial is NOT the temperature of the blown air. Rather it's the temperature you've set for the inside of your car. It's up to the climate control system to achieve this in whatever way it sees fit. Personally, 18 deg C is plenty cool enough for me, even on the hottest day.
We'll see when (or if) summer comes around next year...
