Telltale have just posted the English version of an interview with Dave Grossman that first appeared in the Belgian gaming magazine PC Gameplay Benelux in November;
As I recall, the way it happened was that Tim Schafer and I were fresh off of Monkey Island 2 and ready to lead our own project... The [Maniac Mansion] license fit reasonably well with our collective sense of humor, and I think there was the feeling that having it nominally be a sequel would keep us from going too far off the deep end. So we worked on the design for a while and then presented it to the rest of the all-powerful project leader group, who recognized its merits. We were advised to cut five characters and three locations, which was a fairly standard thing to be told and we were ready for it. I think it took under a half hour to make the cuts to the design, and then we went ahead and built it.Dave also riffs on Sierra, LucasArts in general and of course Telltale.
Source: Telltale Games