If the DLCs aren't meant to be played in any specific order, then why does OWB end with the narration (ending narration spoiler coming up):

Fair Point, I noticed that aswell :shrug:

Well, it is presumably foreshadowing for Lonesome Road, but I guess it could also apply to the battle at Hoover Dam if you ignore LR. Nice spot. :thumbsup:

It probably is just an error, but:

I know it's a long shot, but couldn't they add a script which wouldn't allow you to access LR before OWB, or any of the others for that matter(besides HH)?

They can't do that. They can't sell a DLC but make the content inaccessible unless you buy another DLC. That's going to piss people off, especially if someone could only afford to buy one DLC and chose Lonesome Road thinking it would be playable.

the same thing applies with Eljiah amd OWB

How do you figure? Elijah was only seen in OWB as journal pages and what he left on his trek to Dead Money.

What? There's no chronological conflict here.

Unless you're referring to the fact that the Courier will say "I've never heard of such a place." when Elijah talks about the Big Empty in Dead Money, even if you've completed OWB first.
If you've completed OWB before DM, then the Courier's reply here has to be taken as the Courier lying to Elijah about his knowledge of Big MT (Or that he's an idiot and doesn't get what Elijah's referring to. Or that he has amnesia). That's the only inconsistency I'm aware of.