The Gouda recipe that I'm familiar with dispenses with the initial direct heating stage, and instead relies on the hot water washes to also increase the temperature. The reason for this reportedly has to do with the traditional wooden vats that offered no possibility of external heating.
Two separate warm water additions are typically employed, each time after removing about a third of the volume of the milk volume as whey. ( I.e. if you kicked off with 10L of milk, draw off about 3L of whey and then slowly add 60-70degC water cup-by-cup while stirring until the vat reaches 35degC. Stir for a few mins, then repeat by removing another 3L of whey and again adding hot water to achieve 38degC.
The related American cheese, Colby, differs a bit from Gouda in that it employs a single cold wash, and also only after removing just about all the whey.
Sorry - just realized I'm rambling on without really answering your question. I can only speculate that what is important in the end is the dilution of the whey. The more dilute the whey, the milder or "sweeter" the cheese.
