No, I'm not Italian.
I'm not really into folding bikes so I don't actually really know why people own them in the first place (except for commuting on trains and storage issues). I can only assume that the people in Milan don't have a practical need for them. Most seem to lock their bikes up outside. I keep one of my bikes in my cantina and the other in my dining room.
Thanks for the info - I usually ride down via Vigevano and via Valenza.