I think it is normal, and probably a combination of Airbus programming (the 340 being the largest, it's the most noticeable) and the flight paths around SCL.

I noticed this too, when switching from KLM (734) to bmi (321) on LHR-AMS. You seem to spend quite a lot of time under the clouds departing from LHR, and the 321 seems at times almost to be drifting. I understand that one of the attractions of Airbus for airlines is the fuel economy, and that part of this is the ability to calculate the minimum thrust needed for take-off (with a safety margin, of course) and stick to it.