New Vegas didn't hide specifically tough/dangerous characters or creatures at the start of the game. They actually loaded them into areas where they didn't want the player going right away.

However, the rest of the game scaled in a similar way as Fallout 3. The game locked an area level when you entered it, and you could come back at a higher level and have an easier go of things. Random encounters had a base level that was somewhat tethered to the character level up to a certain point, where the baddies hit their own level cap.

At higher levels newer and more challenging bad guys, either new monster, ghoul, robot types, or new weapons and armor, showed up.

The result is as you described. The feeling, and reality, that the player was vulnerable and needed to tactical at the beginning of the game. By the end, the player was damned skilled, deadly, and could rightly kick the ass of those who got in the way. That is the way it should be. That is what they are trying for in Skyrim... some balance of that, with a little NV too tough to handle creatures and locations thrown in for good measure.