According to Obsidian it is slightly smaller then FO3, but more is being packed into the map.
He most likely meant more content. So quests, locations, things to do, etc etc etc.
This seems to be a trend with Bethesda's games. (I realize New Vegas is being done by Obsidian.) Smaller maps but much more content and activity on those maps, starting with Daggerfall and shrinking steadily ever since. I remember when Fallout 3 was being discussed and it came out that the world map would be smaller than Oblivion, and people got upset over it. The point is walking across endless grass fields and forests isn't that great if there is nothing to DO in them. You could walk quite a ways in Oblivion with no points of interest popping up on your compass, but rarely are you anywhere in Fallout 3 that your compass is not pointing out 2 or 3 interesting things to explore in various directions.
http://i.imgur.com/uBWCz.jpg
That's not really a good thing.
It is a good thing if they packed in more points of interest and activities within the world map. Slightly smaller is easily forgiven (and not really noticed) if you are constantly finding new and exciting buildings or areas to explore. Maybe the Mojave desert is vast, but you'll constantly find interesting things like an abandoned gecko hunter's shack, or a radscorpion cave, or an underground spring. I don't think any of these things would necessarily be improved upon by forcing the player to walk a lot farther to get to any of them.
Point of fact is that in a development cycle, there is only time to design, create, and balance only so many points of interest. Now you are faced with one of two choices - space that content out over a large map, forcing the player to go for long periods without anything exciting happening and potentially becoming bored, or compress all that content onto a smaller map, and ensure that no matter where the player is in your game world, he or she is never more than a minute away from something fun to do. Option two seems like the hands down winner to me.
Just Cause 2 had one of the biggest maps ever, but a lot of the areas were pretty copy-and-paste. There were very few spots on the map that offered something unique that couldn't be done somewhere else. I enjoyed the game well enough, but eventually became bored spending forever getting somewhere only to see more of the same.