I disagree with fsm nutter and mab.
The liquid only seems to cool quicker. It's hotter to start with as it hasn't had the coolant of the milk added.
If the milk is added immediately then the temperature drops suddenly and subsequent cooling is done at a steady rate. The drink without milk rapidly loses it's first bit of heat then slows down.
Then if my drink and OH drink is made at the same time, both with milk added at time of making then mine will be cooler.
oH cup is tall and thick walled, mine is smaller with a wider open top thus the heat will evaporate quicker.
Then if OH takes his outside while chopping wood, his will cool quicker than mine being cupped in both hands in front of the log burner