Regardless of how many actual locations are, the maps are the same size, but New Vegas doesn't use like a third of its map. All that space is filled with locations and things to find in FO3.
NV also feels a little weak in terms of random encounters keeping things interesting.
Also, guys, people love to say that "New Vegas is bigger than Fallout 3" but take the Explorer perk and then look at the damn world map. There's SO MUCH dead space on both the western and eastern edges that is just totally devoid of any locations, or indeed anything but cliffs. It's literally there for no reason.