Massachusetts is very big as well... sure the cities will still be more "cramped" than they were in the originals but it's better than having them all super-duper cramped into a single sandbox.
I suppose that could work, but I don't like the idea of them doing the entire country anyway... eventually they'd have to resort to going back to the West and I don't even want to imagine how much backlash they'd get...
Massachusetts is not that big, having the map node system will bring back the feeling of being in a wasteland as in having settlements surrounded with many miles if not hundreds of miles of wasteland. Fallout 3 settlements are just over every hill. Can't throw a hand grenade without hitting the next location. New Vegas does little better but it still feels cramped.
America is very large. North America is even bigger. New Vegas mentions NCR in Mexico and I don't see why Fallout has to stop at the US/Canada boarder. Canada was apart of America in Fallout. There are still large parts of the Midwest to do as well as the south, Florida and Texas. Chicago was mentiona and I would not mind going back to the locations of Tactics to see the MWBoS again, it has been 80 years.
Even with the Map Node System, it would be many games before America is covered and a very long time before Bethesda runs out of locations and goes to California.
One City at a time does not give me the feel that things are changing on a grand scale. Things changed in the Originals it meant things were changing on a continental scale, effecting thousands if not millions. This is not so much a problem with New Vegas because the story effects two of the Largest Factions and has big changes but it would be nice to go into Arizona or Colorado and not just stuck in the 50 mile radius of one city.
I also have an odd feeling that what ever city Bethesda picks will look just fine and almost every landmark will be intact just like DC in Fallout 3.
Edit: does not mean I will be unhappy with FO4 if it is just based on one city, its just that we can have many cities with the map node system.