Just remember that they could easily make the map bigger, but then everything would be too bloody far away from eachother. Yeah a big map is good, but one that is detailed and has a bit of life to it is much better.
We also need to remember that a lot of what happened in Fallout 3 happened under ground. The metros were absolutely enormous, so pretty much doubled the size of the DC area map.
The key issue with a Fallout game has always been things to do. For example, one evening I decided to venture into one of the buildings hidden at the back of the White House. I ended up discovering Sidney (could have been Sydney) any way, a woman with an attitude. Thankfully due to me exploring another building I found out that her father had died whilst holed up in a hotel trying to find her. She thought he had abandoned her but no, his "Moonbeam" had it all wrong.
That was just one tiny slice of what you got if you explored Fallout 3 properly. There were easter eggs and mini quests absolutely everywhere. The Keller Family Transcripts for example which led you to the Experimental MIRV took ages to complete because you needed all of the transcript holotapes.
Any way, might be getting to the TL;DR point but what ho... In New Vegas the main thing that crippled the game was its actual detail. For example you go to an airport which looks awesome and could have contained an amazing story but no, every building is locked and it's literally just a flat runway with a couple of rad scorpions on it
Fallout 4 can have a tiny tiny map. It's how much detail and content that has been coded into that map that is important.
And from the time they have spent on dev? 5-7 years apparently, this should be absolutely mind blowing.
I can't wait for the game to come out and shut every one up. As soon as you pick your first lock or hack your first computer terminal you're going to be hooked.
So stop the whining and nay saying.