Well there's a big disconnect between the SouthWest and NorthEast side of the map. The 15 is fucked, remember. And the courier needs 2k caps to get into Vegas. It could had been done to get the courier back to Primm again and make primm more lively (there's no reason why the big ass hotel shouldn't be the main building where everything is instead of that weird casino).
Their could be a quest from the Mojave Outpost to deliver something to the NCR guy. Of course you can also betray the NCR. There could be a quest to deliver payroll from the NCR in Vegas to say, Primm or even whatsthatmining town name, could be a cowboy movie like thing. So on and so on.