They're not a deathtrap once you know what you're doing. But when you first start playing the game, if you go any direction other then south, it's a 100% death trap. And even when you do know what you're doing, a low level character will have little to no chance when confronted by Cazadores, Giant Radscorpions and Deathclaws. Sneak isn't very effective until 50-60, and the weapons you get are ineffective against heavily armored foes. Certainly, if you use vats correctly to debilitate your enemies (shooting legs/wings), you might be able to run past, but you'll more then likely run into something else. I've made the run, in fact, I made a character a couple weeks ago, that went into The Divide at level 2, and managed to get almost all the way to the end (where he was assaulted by 3 deathclaws, and I can guarantee that at that point there was no way to kill them).
So, if you don't want your first few hours of the game to be a harrowing mess full of saving, loading and dying, you're forced to go south to primm, then south along the road past the police station, either past or into mojave outpost, around past Nipton (again, you can go off the beaten path, but you'll probably run into Giant Scorps, that can be really annoying at low levels), and then up to Novac.
I've started more new characters then I can remember, 20-30 at least, and 90% of them have gone the beaten path just because it's the most natural way to go. You just don't start with the ammo/supplies required to play the game in any other way, and if you're playing a melee character, good fucking luck going north.
It's a railroad.