There are companions in Vanilla Nevada, they are just to the end of the Vault Questline:
One eyebot that stays with you (if you have the play after storyline perk), and a guard that can be exploited to stay with you iirc. So depending on how you play, after half or the end of the game.
Sonora has mostly temporary Companions (read, they leave after a while when they reach their quest destination) with one relativly half/lategame exception again, wich can also easily be overlooked imo. xD
So yea, to get the most out of you companions, you want to get the Play after Endgame Perk and tackle all optional quests near/after the endgame, wich is sometimes strange ^^"