Hi, I'm H Hoffman - I took the photos/wrote the article. John let me know about the thread here and I thought I should add a bit of information...
After 3 years studying food at the University of Gastronomic Sciences in Italy I have a reasonable knowledge of cheesemaking but probably not much compared to you guys who actually make cheese. I spent a couple of days specifically on Parmigiano-Reggiano with their consortium and then another week with the Grana Padano consortium. This was all a great experience although probably some of you guys would have got even more out of it!
Anyway, one factor which I haven't seen mentioned in your queries on why the cheese doesn't need to be pressed is the issue of the curd size. Both these cheeses have the curd cut really fine - they describe "rice-size" grains. I though there was a picture showing that but when I checked it was not one of the ones I had put up. Here is that...
He's showing how the curd pieces can be pressed together - you can see the size of the curd pieces on his right hand.
As far as I recall the finer the curd is cut, the less moisture is retained - so maybe that's why it doesn't need pressing - but I could be wrong as the theory is never easy to learn when you're not applying it.
Let me know if you have any other questions I might be able to answer.